The easiest way to test if there is an issue with the microphone on your phone is to attempt to make a voice recording using a preinstalled application.
On Android, this is commonly called Voice Recorder, while on iPhone, this is called Voice Memos.
Please make some recordings to the best of your ability speaking into the phone, just like you are on a call, and while having the phone lay on a table.
On playback, listen for any issues with the sound.
If the sound is muffled or scratchy at all, please check that the microphone is not obscured, blocked or clogged. Often, warranty returns for microphone issues are resolved by simply cleaning the microphone on the device.
Please also double check that your phone case is not covering the microphone, or that you may be holding the phone in a way that is also covering the microphone.
If you are only experiencing microphone issues during phone calls, this may be related to your network, or the network reception for the person on the other end of the call.
Past this, if you continue to experience issues with the microphone on your device, please feel free to contact our Support Team here with the issue you are experiencing as well as any relevant photos or videos.