I've gone back and forth on this topic for a while now. Thought he was asexual for a bit, thought he might be gay, but I think the answer to why he is this way might be a bit more complicated.
Phil has a weird relationship with adulthood and maturity. He really wants to be seen as an adult, to be respected for his maturity and knowledge without actually being mature or particularly knowledgeable or wise. We see this going back even to his earlier content, he referred to himself as a mature adult with a buisness degree and always has used words like "immature" and "kid" in a derogatory way, without realizing his attitudes towards sex and sexuality make him seem like an adolescent struggling with puberty.
I don't think Phil has the emotional maturity to even know himself what his sexuality is, and he can't seem to piece it together. I think we all universally have had the experience of being an adolescent and feeling the insecurities around our bodies and the bodies of others, and being confused and unsure of those feelings. Part of growing into adulthood is managing those uncomfortable feelings and understanding who we are, and what that means. Phil has shown he will consistently avoid uncomfortable things, and lacks the self awareness that comes with the discomfort of self reflection.
I think speculation about his sexuality while very funny is moot. I don't think Phil knows what his preferences are, because Phil is emotionally a child, and if you can think back that far and remember how uncomfortable you started getting as your body started to mature and compare how you acted to how Phil acts now, I think you'd see a lot of similarities.
While I don't know if he is actually gay, he is 100% a massive faggot.