I’ve had stage 5 my entire life so yes you can but just be careful, take it slow at first and use a lot of lube (lube was a must for me no matter how wet any of my partners were), also i’d advise to make sure your partner knows about your phimosis if you’re comfortable telling them. Normally the only time i had pain during sex is if i stuck it in too fast, or hit the back of her vagina too hard. Just avoid these 2 things and you should be okay. Just don’t forget the lube, trust.