Phimosis has a number of treatments, one of which is circumcision.
If you can retract the foreskin, but it gets stuck behind the glans: this is the dangerous form of phimosis and you need to be aware of what to do if the foreskin gets stuck -- seriously, you risk penile amputation if you don't get help immediately in this medical emergency.
If the phimosis is tighter you just have a foreskin that doesn't retract. This puts you at a very slightly increased risk of penile cancer (but a tiny increase on a very small risk probably isn't enough to cause surgery).
Most sexual partners either won't care; or will find it cute and interesting.
Surgery is carried out usually under a local. The surgery is pain free. You're given lots of pain meds for the days after, and some anti inflamatories. There's an impressive amount of swelling for maybe a week.
One thing that some people find weird is that you'll need to pee in the hospital after the surgery. Since you've lived your life with the sensation of pee on the foreskin you think it's going to be v painful, but apparently it really isn't.
Men get themselves into all sorts of bother over their knobs, and really a cock is a cock is a cock.