There's an issue with my iPhone 7 Plus where the speaker and microphone don't seem to work. When the phone is restarted, the audio usually works for one call and then stops working again. Apple support claims it is a hardware issue, but one of the local tech shops say that they've gotten several iPhones with the same problem and they've replaced various hardware components without success. Also if it is hardware, why would it work once and then stop? The calls work perfectly one time. To test the microphone, I've been opening voice memo and recording, which seems to work for a short bit after the phone is restarted, but then I get a "no audio device found" error. Tried factory resetting without success.
All the network settings work, I have also tried every reset option. One thing that hasn't been tested yet is plugging in headphones and seeing if sound and voice is picked up through those. Planning on testing that soon. Whether that works or not what would that determine?
The iPhone is running iOS 12.3.1, model number MNR42LL/A.