Phimosis treatment

I think my boyfriend has phimosis, because he can't pull his foreskin back when his penis is erect. I don't know if it will go back when flaccid. We have normal sex and he doesn't feel any pain, unless he pulls it right back he says it gets painful. I have noticed after sex when he pulls out of me the foreskin has restracted a bit, not fully, and the top looks kind of swollen or kind of like it's being strangled. That's the best way I can put it. He says that doesn't hurt either. If we have normal sex and he doesn't feel any pain, does he need to see someone about it?