A PhD is a Doctor of Philosophy, so unless that PhD has been invalidated he is in fact a doctor. I don't know his personal preferences so perhaps he doesn't lik

A PhD is a Doctor of Philosophy, so unless that PhD has been invalidated he is in fact a doctor. I don't know his personal preferences so perhaps he doesn't like to be referred to as a doctor (based solely on what you're saying). But there was nothing factually incorrect about the poster saying "Dr. Hipp."