There is no direct relation to POIS. It's a physical condition, that can be seen early on in childhood. I have, or rather had phimosis since a few months ago.
What I did was, every day I would pull my skin back as far as I could go for about 5 minutes. Eventually, after 3-4 months, I was able to pull it all the way back over the mushroom.
The problem with Phimosis is that the head is HYPER sensitive, even the slightest touch will HURT. What I recommend doing is, when you have the head exposed (which may take a while to begin with) use the shower head to spray water on when you shower.
Good luck! Don't resort to surgery, I've heard bad things about circumcision this late in life.