At least it is if we’re going to accept a definition of transphobia as ludicrously wide as this:
Transphobia, like homophobia and biphobia, is an umbrella term to describe various negative attitudes towards people based on a single characteristic: who they love, or who they are.
You can be perfectly pleasant to trans, gay or bi people and still be transphobic, homophobic or biphobic; you can vote for equal marriage but feel uncomfortable around gay people, use trans people’s pronouns but think they’re mentally ill, accept that bisexual people exist but believe that bisexuality means promiscuity or sexual greed.
So too with homophobia, biphobia and even racism.
Having negative attitudes about other people is the basis of being human. We’re tribal animals. We work on ingroup and outgroup. That’s simply what we do and who we are. We also often enough have positive ideas about others but the negative is implicit in that, innit?
With a certain amount of training and civilisation we’re able to get to perfectly pleasant, tolerance. To insist that our not going further is a phobia is ludicrous. It’s a denial of how humans work.
And seriously, is someone really, really, trying to insist that thinking some other person is a nutter is a phobia?