Hope this helps? The wives of British monarchs tend to receive the ceremonial title of queen—or, more specifically, queen consort. For example, the Elizabeth's mother (also Elizabeth) became queen consort when her husband, George VI became King. Duchess Kate will likely become Queen Catherine when William ascends to the throne. Camilla could become queen consort, though for now Clarence House has announced that "It is intended that Mrs. Parker Bowles should use the title HRH The Princess Consort when The Prince of Wales accedes to The Throne." However, the reciprocal is not true. Men married to the British monarch are known as prince consorts, not king consorts. As with many royal traditions, you can chalk this one up to a very old and powerful patriarchy. Kings always reign, whereas Queen can be a symbolic title.
And,
(1) QUEEN AS CONSORT/WIFE
Queen, as a term, has its origins in an ancient Germanic word for “wife”. So while the word king specifically means ruler, the word queen came into English to mean specifically “the wife of a ruler”.
This is what we would, today, clarify as a queen consort: the wife of a king, for example, Alexandra (wife of the King Edward VII) referred to while he was on the throne as “The Queen” and, after his death, as a respectful courtesy “Queen Alexandra”. Likewise, Mary of Teck, (wife of the King George V) referred to as “The Queen and, after his death, as a respectful courtesy, “Queen Mary”.
This is all in line with the original meaning of the term Queen as “wife of the king”.
To differentiate in formal analytic writing from the meanings below, we might refer to such a person as “Queen Consort”.
(2) QUEEN AS SOVEREIGN
Now, the complex bit comes historically with those rare cases when a woman inherited the throne. Bear in mind that in England, Great Britain and then the UK historically it was considered unlikely a woman would inherit the throne, given the custom and rule of male-preferred primogeniture, which means that the heir to the throne is the eldest living son of the present king (and any of their children), then any other sons (and their children), before any daughters. That is, a woman could only succeed to the throne if she had no living brothers at all, and no deceased brothers who left surviving legitimate descendants. (This was altered as recently as 2012 to allow the eldest child, regardless of gender, to inherit, which will make a woman sovereign far more likely than it has ever been in the past).
The term Queen is used here differently, meaning, according to the Oxford English Dictionary, “A female ruler of an independent state, people, etc., esp. one who inherits the position by right of birth; a female sovereign. Frequently with the, as a title”
To differentiate this kind of Queen (sovereign) from the other kind (wife of a king), today we sometimes use the term “Queen Regnant” in analytical writing, meaning “Reigning Queen”.
(3) QUEEN AS A TITLE OF COURTESY AND RESPECT
Briefly, it’s worth mentioning that there are a few uses of Queen as a courtesy exclusively for the wives of Kings who have died. The usual case is that they are no longer referred to as “The Queen” the moment their husband has died, but out of respect they are called “Queen x” (e.g., Queen Alexandra, Queen Mary, Queen Charlotte) and they are technically a “Dowager Queen”.
If one is also the mother of the next monarch, they may be known as “Queen Mother”. Only one has publicly/regularly been known as the “Queen Mother” (the mother of the present monarch, known as “Queen Elizabeth, the Queen Mother”, because the fact that she had the same name as her daughter would have caused enormous confusion if there were two Queen Elizabeths in public life (i.e., *The* Queen, and the dowager queen).
The term Queen Mother is part of English public speech because it has been used in the Anglican Church Book of Common Prayer which includes prayers for the “Mary, the Queen Mother” and “Alexandra, the Queen Mother”. It is assumed that is is from here where the term for Elizabeth was derived. Beyond that, it is not an official or legal term, and has not been widely used outside of church in the past, precisely because the name (e.g., Queen Mary) was sufficient to identify the former queen.
FINALLY(!) WHY IS PHILIP NOT KING
Short answer: because his wife is the type of Queen described as (2) above (reigning) and not (1) above (wife of a king).
There is no recognised title for the husband of a king in the UK (or previously in England and Scotland), although there have been a few interesting anomalies described below.
One of the reasons for the fact that there are both no prescribed titles and that there are several anomalies is because, as mentioned above, women were unlikely to inherit the throne.
Some examples and anomalies (and several Marys)
Queen Mary I: The first, genuine and undisputed woman sovereign in England was Mary I (daughter of Henry VIII). What to call her? As there was no precedent, the most appropriate name to be used for a woman in this circumstance is “Queen” (the term usually used for the highest woman in the land, even though that woman normally is the wife of a sovereign).
Mary married the son of the Holy Roman Emperor, Prince Philip Hapsburg of Spain in 1554. Philip, as a man, wanted at least co-rule with his wife and there was precedent for this in England at the time. A common law rule called “jure uxoris” allowed a husband access to noble titles (e.g., Earl of Warwick) by “right of his wife”—that is, a woman inherits the title as the sole heir of her father, but she does not rule, her husband rules in her place—the property, titles, responsibilities, etc. of a woman become her husband’s the moment they are married. This rule meant Philip would be called “King of England”. This was not widely acceptable to the English peers and to parliament (because Philip was due to become King of Spain which could mean England lost its own sovereignty to Spain), so to compromise this appropriately, some limitations were put in place by an act of parliament, which included (a) to acknowledge that it was “by right of his wife”, for the first time Parliamentary documents, declarations, etc. would be made with BOTH THEIR NAMES, (b) he could not continue as King after her death—his sovereignty would only be for HER lifetime (which turned out to be 4 more years).
Mary, Queen of Scots: Now in Scotland, Queen Mary of Scots declared her husband Lord Darnley “King of Scots”, however she actually had no right to do so, and it was not recognised. Sovereignty was understood to rest with her alone (until she was deposed).
Elizabeth I: The next sovereign in England, of course, is Elizabeth I, who never married and this is where in England we see the term “Queen” move most explicitly from one meaning “wife of the sovereign” to one meaning “woman who reigns”. The length and notoriety of her reign brings the meaning of the term “Queen” directly to mean “A female ruler”.
William and Mary: King William III and Queen Mary II ruled as Britain’s only genuine, equal co-rulers. This was another unique case, whereby William III ruled by invitation of Parliament (his predecessor was James II who had fled the country and thereby left the throne vacant), but James’ daughter was also the wife of William III. This solidified the monarchy at a time when it may have been lost—appeasing those who expected continuity by inheritance and those who wanted parliament’s decision to bring in a “good King”. Either could continue as monarch after the death of the other. In this case, William was not “king by right of his wife” but King in his own right with Mary as Queen in her own right. The only time this has occurred.
Victoria: Victoria wanted to make Prince Albert King of the United Kingdom alongside her (presumably in a “William and Mary” model, although this was unacceptable to Parliament and to the peers, particularly because he was a prince of a rather low-status Germanic state. The specific title “Prince Consort” was developed for his use, although it has never been used again.
Elizabeth II: Although several television dramatisations have emphasised the idea the Prince Philip, Duke of Edinburgh was jealous of his wife’s role, titles, etc., this is mostly dramatisation. My understanding, from a historical and constitutional perspective, is that it is remarkably well-understood that in British law there is no specific title for the husband of a Queen (Queen Regnant), and that although he was made a Royal Duke at the time of his marriage and created specifically a British Prince in his own right a decade or so later, there was never any possibility of his being named King, no desire for it among any party.