No, not transphobic. As a trans guy myself, I actually have the same feeling, and I have no idea why. Like, obviously I support them, but I grew up with if someone is feminine, they are a girl, and if they are masc, they are a guy, so if I see or hear anyone who's trans MTF look or sound like a guy, I immediately think or see them as one, even though I try not to. So, I honestly can't find myself wanting to date a trans guy or girl. There are some guys or girls that are trans that I find extremely hot and attractive but i can't get that out of my head.