It’s canon that Denobulans live F O R E V E R and that Phlox has been a doctor for at least 46 years when he joins the crew of ENT so Trip is falling for an older man. He promised he’d never do that again when Archer turned him down but what can you do.
Trip seems the most invested in Earth culture of the crew so Phlox probably originally approaches him to talk about that but then it just kinda becomes a thing really casually and slowly until Trip stumbles all over himself and finally makes it a real thing. Phlox isn’t any good at approaching that stuff either cuz 1. that one episode where he has no idea if that girl is into him and then also 2. Denobulan men are sexually inhibited and that’s canon












