Possible steps to resolve not being able to hear a caller on the phone:

1. Check your phone’s volume settings.
2. Check your phone settings for a volume boost switch.
3. Check if the caller has their sound or volume turned too low.
4. Check the sound quality by asking the caller to repeat something.
5. Check any headsets or earbuds that are in use and ensure they are plugged in correctly.
6. Check that the speaker and microphone on the phone are not blocked or damaged.
7. Install any updates to the phone’s system or app you are using.
8. Confirm the phone call is made over wifi or by signal.