Not being able to hear some one or them not being able to hear you disables the basic purpose a phone, below are some troubleshooting steps to help fix the issue.
Note: Some Settings, Menus, or Icons may differ from that of your device depending on your software version and wireless service provider.
If your speaker or receiver sound gargled or are not working at all, the following step:
Ensure the phones volume is turned up.
Ensure that the phone is not playing through a wired or bluetooth headset
Check the speaker or receiver are clean, and not obstructed (If your phone has a removable back cover, take it off an clean the speaker)
Turn the phone off and on again.
Check for a software update
Try to clear the cache on the app having issues
Some softwares may help resolve or at least detect the issue, open the play store and search for "audio fix" any of the software available may help.
Android only:
If the steps above were not able to fix the issue, you are welcome to send the phone in for Repairs or check with your carrier for insurance options.
