If you are interested in a person you assume to be cis, and they have had bottom surgery so the only real way to tell if they are trans is if they tell you, and finding that out makes you decide against having sex with them, you're a transphobe.
If you are interested in a person who is trans but has not had bottom surgery, and that makes you not want to have sex with them because you are not attracted to penises/vaginas/etc., you are not a transphobic
I don't think any trans-related surgery is necessary unless the person feels it's necessary. I've had tons of people try to talk me out of FFS and tell me I don't need it, but I know what I need and no one is gonna convince otherwise. On the opposite end, there are plenty of trans people who don't get bottom surgery by choice and that's perfectly fine
As for the genital preference, honestly I'm pan and I'm attracted to really any kind of genitals, even ambiguous ones. I don't really know what it's even like to have a genital preferences I'm not going to say it's wrong to have one.