The Company Phone
The organizations that offer a company phone to their employees often expect them to keep those cell phones on at all times. We have nothing against this policy if their work requires it. However, one thing is quite simple; there is no need to keep the company phone active after work hours.
Apparently, this supervisor thought otherwise because they reached out to this OP to inquire about the company phone after their shift. We believe everyone no matter how important their job is, should have time to relax when they are not at the office.