There is quite a big difference between not wanting to date a girl because you’re not into girls and not wanting to date a post-op trans woman who looks, sounds, acts, feels, and smells exactly like a girl because you stubbornly insist that “trans women are not real women.” In the latter case, your reasoning would indeed be transphobic.

But I nevertheless believe that, so long as it’s specifically limited to a romantic preference and doesn’t leak out into, say, stuff like who should be allowed in which locker rooms or whatever, it’s not one of those things where it’s at all fair to call the person “a transphobe,” even if they do technically hold a transphobic belief that animates their romantic preference. I reason that it’s kind of like what a lawyer would call a “public policy exception:” It’s much more important to avoid deterring anyone from holding any romantic preference for any reason than it is to fight bigotry in the world. Romantic preferences just really ought to be sacred.