The British monarchy is strictly hereditary.
Prince Philip is not in the line of succession for the British Monarchy. Queen Elizabeth is. She is the reigning Queen.
It's true that when a King marries, his wife is called the Queen. However, she is not a reigning Queen but a Queen consort. If her husband dies, she has no claim to the crown.
However, it sounds very odd to talk of a King Consort; so the reigning Queen's husband is not called a King Consort, but a Prince.
Just a peculiarity of history and the English language.