Did you read the original reddit thread? Chasers are dangerous to the trans community. It isn't about being attracted to trans individuals, it's about specifically seeking them out for being trans and fetishizing them being trans.
Can you not see how this may look if you are the trans person in this relationship?
I'm not stupid, I know it means "fear of." Do you think Homophobes are "afraid" of gay people? What abiut transphobes? In the context of bigotry, phobia is used to refer to invalidating or undermining ones sexuality, gender identity, etc.
Literally talk to a trans person, or just read through that thread, it isn't difficult.
Talk to trans people about how they feel about lumping anti-trans views into the "transphile" category because rather than being hated outright, chasers simply prey on trans individuals and undermine their gender identity in a sickeningly fetishizing way.
This is the most bizarre stand I've seen someone take online, and that's really saying something. Phobic means an irrational fear or disgust off something, these people are clearly neither afraid or disgusted of trans people.