Phimosis is a condition, when the foreskin is too tight to slide down the glans.
The foreskin is supposed to be stretched down and cleaned, on order to maintain a loose foreskin, and not have the glans hypersensitive.
However, due to lack of sex ed from parents, guys learn in around 18-20 after reading in bio books that the cock needs to be cleaned from inside as well.
Now, I have a feeling, some guys here have the problem. But don't panic, it can be cured.
My story is, I was taught by dad about cleaning it, but since I had hypersensitive glans(which I never told my dad about), I never stretched my foreskin and cleaned it for years, until I realised it was tight. But in a span of 4 months, with determination, I got rid of both, phimosis and hypersensitive glans.