Queen Mab is the Queen of the fairies in a long speech delived by Mercutio in the play Romeo and Juliet. There may also be other works which have the name of this fairy as a title. But if you are thinking of the speech, it was written by William Shakespeare.
There was no such title in ancient Egypt - you are thinking of "King's Great Wife", which can simply mean a queen but often refers to the favourite, first or foremost of a pharaoh's many wives. Another title used by the principal wife was "Mistress of the Two lands".
Because the title 'King' outranks the title of 'Queen'. Elizabeth is Queen Regnant, meaning she is not Queen through marriage etc... but Queen in her own right. Phillip is not a King in his own right, and therefore he is given the lesser title of 'Prince Consort'.