I don't think there is a universally agreed definition of transphobia anymore @Elendon.
It's not just the obvious stuff like hatred, poor treatment, or broad stereotypes about a group of people. I think it's becoming any situation or comment that could potentially trigger someone's dysphoria or upset them in any way.
It's any comment that says you can't be a woman if you have a penis, for example, or suggests that gender isn't a feeling, or labels someone as a "transwoman" instead of "just" a woman. Many things on this thread would be labelled transphobic elsewhere.
It's how conversations like this are routinely shut down and why situations like this one will become increasingly commonplace.