Here is a list of things that can help to resolve the issue:

1. Check if the ringer volume of the phone is turned on.

2. Check the ringtone setup and make sure it is not set to vibrate or silent.

3. Confirm if the caller is calling from the same network or a different network.

4. Make sure the phone’s battery is not discharged.

5. Check if the phone’s network connection is stable.

6. If possible, have the caller try toong a different phone.