There is no room for socially conservative views in a socialist left-wing party. Period.
Well, that's Galloway and his Workers Party told, then.
trans women are not biologically women
They are not. Saying so does not make one transphobic.
the trans rights movement arguably is the socially conservative position,
It does accept that sex is binary - but that some people are somehow born into the 'wrong' body (an impossibility). From the point of view of those who identify as non-binary, gender fluid and all the other gender identities, trans is conservative.
There's nothing wrong with supporting trans rights. The problem comes when those rights conflict with the rights of others (eg the rights of women who want single sex spaces). Trying to resolve these conflicting rights should be approached in a spirit of compromise not in a spirit of rigid demands and name calling.