Transphobia is a persistent unreasoning fear of, or antipathy toward, transgender persons and cross-gender expression. The concept came into use to explain the fact that some people “freak out” and commit hate crimes against transgender persons. Why do they “freak out”? The most plausible theory is that, in large part, they’ve learned (mistakenly in my opinion) that God finds crossdressing disgusting. At some level, they’ve incorporated such dubious notions into their mental functioning and thought processes. They have internalized those ideas through learning processes and contact with parents, teachers, pastors, or others who share such notions.
Transphobia is not a quality of TRANSGENDER persons (except by sad coincidence), just as homophobia is not a quality of homosexuals (except by sad coincidence). Rather, these ordinarily are qualities of OTHERS whose persistent loathing and fear may motivate them to engage in hateful speech, physical assaults, or even worse.
When we treat transphobia as fundamentally a quality of TRANSGENDER persons, as I’ve seen some do on this forum, we miss the significance of the concept. Prejudice and discrimination against transgender persons is motivated by something or other; and that “something or other” has been given the label “transphobia.” To be sure, crossdressers who seek counseling because they feel guilty about their crossdressing or cross-gender feelings may have a mild form of something akin to transphobia; but concern about transphobia within the LGBT communities is mainly about hateful persons who pose a threat to crossdressers, not to crossdressers themselves.
For instance, when teenage transgender person Gwen Araujo (born Edward Araujo) was murdered in Newark California by Michael Magidson and Jose Merél after a party, the young men who murdered her clearly were transphobic. They claimed at their trial that they had experienced severe “trans panic” after becoming aware that Gwen was not genetically female. Fortunately, the jury didn’t buy their claim that their fear and loathing of transgender persons or expression was adequate reason to commit murder. It convicted them of second-degree homicide. But note that it was Michael Magidson and Jose Merél who were transphobic. There is no evidence that Gwen was transphobic. On the contrary, she fully accepted herself and was accepted by her mother and siblings as well.