I'm going to ditch my transphobic friend
Why do you want to ditch a friend like that?
I don't want to spend my time with a person who does something disgusting.
That is very powerful that you want to stick to your morals. If they're constantly being hateful to a group you support, it's fair to not want to be around such negativity.
I just feel it is wrong.
It is good to recognize bad behavior in other people. I think you could try to teach them about the issue so they might have some more sympathy.