Prince Philip was not a king because the title of king outranks that of queen. Queen Elizabeth II was born a royal princess who was heiress (presumptive) to her father, King George VI. So it would have been inappropriate for the prince, as a consort, to assume the title of king.
Camilla, the new Queen Consort, may eventually be called "the Queen" for short but is officially a consort because she is not the one crowned as monarch.