1) Ensure the microphones are not being obstructed by something like a phone case/cover.
(The primary mic is located on the bottom right, the secondary mic is located on the top to the right of the speaker key)
2) Blow into the Mics to try and dislodge any buildup of dust/debris that might be lodged inside.
3) Run the device in safe mode and test to see if the audio improves in case of app/compatibility issues.
4) Try a factory reset to restore the phone to its original state.
5) If under the one year manufacturer warranty period contact Kyocera or Verizon for a replacement. Or if you pay for an extended warranty/total equipment coverage on your monthly bill contact Verizon for a replacement.
6) If out of warranty check with a local cell phone/electronics repair shop or the manufacturer for repair options.