I was wondering what are the causes of phimosis?

Inflammation : Inflammation often results in tissue scarring. Recurring bouts of balanitis or foreskin inflammation can result in the tightening of the foreskin. This is known as phimosis. Circumcision is curative.

Most congenital: Foreskin opening remains narrow from birth, forceable retraction of foreskin in childhood which results in skin splitting ; later scarring. Inflammation ;/or foreskin infection especially balanitis xerotica obliterans.