Please try the below:
1. Disable the call mute button if turned on.
2. The phone microphone may be blocked or damaged by foreign objects, dust or debris. Please contact us for further testing and confirmation.
3. Check the signal strength of both the receiver and caller. Poor signals at both ends will affect sound clarity.
4. Use headphones that fit your phone and check if the other party can hear you.
5. Update the system to the latest version.
6. Restart your phone.
If the issue persists, contact our Customer Support for further assistance.