It's too simplistic to say it's transphobic to segregate on sex. Facilities are segregated this way for the safety and dignity of the majority of users. You can't simply throw that out. If it's decided not to segregate this way you have to consider if the facilities are still fit for purpose.
Quite.
If someone states, for their sense of privacy, dignity, safety, identity, beliefs and comfort they do not wish to have to change in front of or shower with people of the same sex then absolutely that should be respected. No one should ever be forced to undress in a situation they feel uncomfortable and pressured in: safeguarding 101.
The answer is to absolutely provide them with alternative private facilities, no fuss, no problem. That's inclusion. That's diversity.
For a person to say for reasons of their sense of privacy, dignity and comfort they insist on being permitted to undress alongside students of the opposite sex who will have to change and shower alongside them regardless of their sense of privacy, dignity, identity, safety, beliefs and comfort.....? And I don't care about their consent?
No.
That is not inclusion, that's something else entirely. Other people have rights too.