Both my brother and my boyfriend had phimosis, however my boyfriend managed to help his by gently stretching his foreskin. You'll want to do this before having sex because you'll need to pull it back to have sex or else you'll be in pain. I would recommend against circumcision; my brother had this when he was very young and he regrets it.
Try gently stretching the foreskin over your head, and you can also buy a cream to help this from your GP. I would recommend seeing your GP regardless, however.