iPhone 6s, iPhone 6s Plus, iPhone SE - Intermittent no audio on calls  

Some customers might report that they experience intermittent no audio issues on their iPhone 6s, iPhone 6s Plus, or iPhone SE, where both the caller and the call recipient can’t hear each other.

Toggling Speaker mode on and off during the call or power cycling the device may temporarily resolve the issue.

1. Verify that the customer is using the device in a known good coverage location, where other devices don’t experience this issue.
2. Check that the latest Carrier setting is installed.
3. Follow the troubleshooting steps in If you can’t hear a person on a call or voicemail or if the sound isn’t clear on your iPhone (HT203800).
4. Follow the troubleshooting steps in Get help with the microphones on your iPhone, iPad, and iPod touch (HT203792).