In the vein of words like homophobia, these words’ definitions are not strictly in line with their etymology. Per every dictionary (but quoting Webster), transphobia is defined as:
irrational fear of, aversion to, or discrimination against transgender people
And this might create some linguistic ambiguity, but I cannot seem to find actual documentation on a medical or psychological fear of transgender people at all. It seems this behavior is entirely (or almost entirely) a learned bigotry.
The other word, “transmisia”, has not really been officially adopted in any circle I can find. The only place I could find it with any prominance is a site called the “Trans Language Primer”, and I know nothing about it (except that it looks like geocities) so I won’t be linking it directly. Suffice to say, they speak negatively of the term (despite defending it as having a good intention) and favor “transphobia” for reasons of clarity.