The Sony LinkBuds S can be used for calls on your smartphone. You can also use these ear buds for video calls.
If you have having issues with low volume or muted audio during calls, then you can take a look at this troubleshooting article from Seeking Tech.
1. To start off, make sure that both the ear phones and the connected device are both turned on and connected to each other.
If you have problems turning on the LinkBuds S, you can check out this guide. For Bluetooth connection issues, you can check out this post.
2. You can also try restarting your phone or other calling device to see if doing so will fix your call audio problems.
3. If you can hear the other person but the volume is too low, then you can try using the volume buttons to make it louder.
4. If you are using an app, then you can try to increase the volume level if you are able to do so from within the application.
5. Make sure that you are wearing the ear buds correctly as you should put them as deep in your ear canals as possible without feeling uncomfortable. Otherwise, the sound output may be partially blocked off.
6. You can also try changing the ear bud tips to make sure that you can get clearer sound output during calls. Keep in mind that the sizes of the left and right ear bud tips to not have to be the same as they only need to feel comfortable in your ear canals.
7. If you are using a video calling app, then you can try searching the settings menu in the application for an option to change speaker and/or microphone setting to Headset (LinkBuds S Hands-Free).
8. Taking off the ear phones, placing them back into charging case and then closing the charging case lid may help fix the call audio problems.
Once you do all of the above, you can take the ear phones back out again and then reconnect it to the other device. Afterwards, you can try testing the call audio volume.
9. Resetting the Sony LinkBuds S may clear up any bugs that may have been causing the call audio to be low or completely muted.
If a regular reset does not seem to be working, then you can try a factory reset. By doing so, the ear phones will be returned to their original factory default settings.
You can check out this tutorial to learn about how you can reset/factory reset these ear buds.