I dunno, I think a fair amount of incels would find asexual people rather frightening. Along with anybody else who dares exist outside of their norms...
However, phobia doesn't necessarily refer to fear. And believe me, I've had that that discussion before with homophobes. One guy I had the displeasure of conversing with claimed that just because he hates gays and thinks they should be outlawed doesn't mean that he is homophobic-- after all, he's a tough guy! He ain't afraid of no gay! It was very facepalm-y. Rather, phobia can also refer to an aversion or strong disdain, and usually erasure gets lumped into that definition when used in the concept of a marginalized group.
And yeah, there is very little fear of asexuals. There's many reasons, though beyond the standard "Everybody's sexuality should be respected types", those reasons are generally terrible. For one, ideological and religious zealots actually tend not to mind asexuals. In part because its difficult to identify an asexual unless they outright tell you. Some may perceive that as an example of a sexual deviant "doing the right thing" by not reproducing, having sex, masturbating, or marrying (even though that's not how asexuality works and its very possible for an asexual to have some interest in sex, masturbation, having children, and/or romance). Sex-aversive and sex-phobic religions and philosophies also lend themselves to viewing asexuals as "pure" due to the perception that asexuals are either born "above" dirty things like sex and/or romance or are effectively straight people who simply do not indulge in the sin of sex. Again, this is not how asexuality works and I would consider it a form of aphobia to falsely elevate asexuals to the pure status, akin to putting women on a pedestal just because they were born with two X chromosomes.
Furthermore, a lot of people don't fear asexuals for the same reason an atheist doesn't fear the wrath of God-- they just straight up don't think they exist. Unlike the existence of god though, healthy sexuality is not something that can be denied without consequences. And asexuality is a healthy sexuality. Asexuals are not straight people who are just above sex/romance. Asexuals are also not homosexuals or sexual deviants who just "do the world a favor" by not acting sexually or romantically. Asexuals can perhaps find Mr. Right someday, but falling in love with one person does not make something not asexual and it is possible that there is no finding Mr. Right because they are not interested in romance. To say otherwise to any of these things is to engage in aphobia. Case closed.
