1. Make sure that nothing is blocking the microphones.
There are 2 microphones on the left headphone and 3 located on the right. If something is blocking the microphones, this may result in your voice sounding quiet or muffled when taking phone calls.
If this is the case, please ensure that nothing is blocking the microphone.
2. Check whether you have the same issue when using the built-in microphone on your device.
3. Enable HD Voice phone calls.
Some carriers allow you to make phone calls over the VoLTE/4G/5G network, which can dramatically increase the sound quality compared to traditional phone calls.
4. Perform a factory reset on the P100.
You can perform a reset on the ear buds by following the steps here.