Do we need to report delayed sleep phase as a long-term health condition, or does it go away after being treated? My teen is getting ready to go to college.

Sleep phase. I don't think this is reportable. However, after successful treatment the person must commit to staying well. This usually involves a fixed rising time and general sleep hygiene. That can be very hard for a college student. Your teen might want to talk to a dorm resident or academic advisor or college health professional on arrival at school for advice on maintaining improved sleep.
Don't know. About reporting, but once better, the problem can stay away with consistent maintenance of appropriate sleep/wake schedule.