I was also in high school in that time period and had a similar experience. As I recall it, pretty much every student had a phone by 2007ish (flip phones back then), and using a phone in class was grounds to have it confiscated for the day and get a detention. This was absolutely enforced.

My college experience was similar to yours as well. All exams were paper (often blue books). Having a phone out would get you kicked out of the exam hall. But by the time I did med school, it was all digital.