I don't think you know what a PhD is!
Mine was on The Synthesis and Nuclear Magnetic Resonance Spectra of Some Difluorophosphino-nitrogen Compounds.
You CAN get a PhD in something like usability engineering of course. (A friend's girl friend is finishing hers just now)
But first you need a first degree - have you got one of them? I've got two first degrees, want to borrow one?
Chemistry or computing, your choice.