Internalized transphobia definitely makes it worse, but I think even in a theoretical society where there is no transphobia, I would think gender dysphoria would still present as a source of distress, and medical transition would still be necessary to help address that distress.
I am skeptical that gender dysphoria is just caused by social stigma or transphobia.
EDIT: I misunderstood Ada's point, I agree with her point that internalized transphobia leads us to reject accepting being trans and leads to not feeling like transition is an acceptable course of action. She never meant that gender dysphoria was caused by internalized transphobia.