I repair iPhones. If you were my customer, I would take the phone back and solve the problem. As part of my repairs, I test all cameras, buttons, microphones, speakers, proximity sensor, screen functionality, charging capability and wifi access BEFORE & AFTER starting & completing works!! To prevent such issues and to find actual damage before I start.
I suggest to all that you carry out own testing before you hand over to repairer. Also make sure passcode is removed or advised to repairer to allow access for these tests!
[BTW - to test proximity sensor, use voice memo and switch speaker icon to white].