Due to its suffix "phobia", I think the most linguistically sensible definition of "homophobia" is "fear of people who are sexually attracted to the same sex". Under this definition, though, the word is pretty much useless, since pretty much nobody is actually afraid of homosexuals or bisexuals. The word would gain some utility if it also included hatred or disgust toward LGB people, but I don't really see a linguistic justification for doing that.

If we're going to be sticklers about the "sexual" in "homosexual"/"bisexual"/"sexual orientation" referring to sex and not gender, then we should probably apply that sort of standard consistently.