I also felt like that. Khemjira is turning 21 and Pharan is 28, so calling phi is more accurate. But subtitles…
But why he told him that? Because they are lovers and because of that Khem is allowed to let the "phi" part away? I mean why not "phi Peem"? Why just Peem? I was confused for a second but Peem is older that Khem , you can see clearly when they are children