The iPhone 7 series of devices have proven to be very unreliable, suffering from flex-based issues similar to the iPhone 6 Plus (Touch Disease). On the iPhone 7, the fault line runs along the top of the SIM card reader and affects mainly the Audio IC.
If you are seeing symptoms like those below, then this could be your problem:
- Voice Memos app / Loudspeaker on call - greyed out
- Siri doesn’t hear you / Caller can’t hear you
- Most other Audio related issues that aren’t solved by modular replacements
- Long boot times (3-5 minutes)
- iTunes detects the phone but stuck on the Apple Logo
This requires a micro-soldering repair and is not DIY.