Seriously, what is with this thread?
Homophobia is not an actual phobic disorder, it's a casual description of the most commonly understood theoretical mechanism behind the relatively extreme reaction many people seem to have to homosexuality.
Unlike people of different races, gay people do not have distinguishing physical features. They could be anyone, which means they could be you. That is the fear, it's not the gay person out there, it's the fear of not really being who you think you are, and the constant intrusive realization that all you'd need to do is stick your dick in another man and suddenly everything you thought you knew about yourself would be meaningless. It's the relative permeability of that line and the consequent instability of ever being truly, definitively heterosexual, because you can't be truly, definitively heterosexual until you've died, all it takes is one slip, one wrong thought, one confusing dream and you stop being the definitive heterosexual that you think you are.
Homophobia does not manifest visibly as fear symptoms, although it may manifest as extreme disgust or anxiety, it manifests as a dislike or hatred. It is, however, a compulsive hatred, it's a hatred which stems from the desire to protect the psyche from its own inability to guaruntee its own heterosexuality. It manifests in the need to symbolically punish or reject people who embody the potential for homosexuality which makes the homophobe uncomfortable.
However "rational" homophobes think they are, there is still the underlying question of why they pick the targets they do, and what produces the fundamental need to structure the world in the way that they do. Even today, we have no problem employing this kind of pseudo-medical thinking in the case of homosexuality itself, we constantly look for "causes" outside of culture for why gay people should exist. Why should we do less for anyone else? Why should we assume that "I hate gays" is less prone to medicalization, as a statement, than "I like boys (or girls)".