Hi, I am sorry you are dealing with phone call audio issues. Does it only do this with phone calls, or does this happen with other applications' audio? There are a few things that can cause issues with the speaker while you are on call or listening to audio playback through your Galaxy phone. For example, there could be an external device where the audio is being redirected. It's also possible that a software problem or physical damage is causing the issue. Give these steps a try: https://www.samsung.com/us/support/troubleshooting/TSG01001255/
Another thing to try is clearing the cache partition on your phone. The steps to do so are:
Performing a wipe cache partition removes any temporary files that may be causing an issue with the device. All personal files and settings are not affected by this option.
- Ensure the device is powered off.
If the device is unresponsive/frozen, press and hold the Power button (located on the upper-left edge) for approximately 10 seconds or until the device power cycles.
- Press and hold the Volume Up button (located on the upper-left edge) and the Home button (located at the bottom in the middle).
- While continuing to hold the Home and Volume Up buttons, press and hold the Power button (located on the right edge) until "RECOVERY BOOTING" appears in the upper left then release all buttons.
- Select wipe cache partition.
Utilize the Volume Up/Down buttons to highlight and the Power button to select.
- Select reboot system now.
Option is highlighted, utilize the Power button to select.
Finally, if these do not help, try using Safe Mode to see if a third party application might be the cause: https://www.samsung.com/us/support/answer/ANS00062983/
Please let me know if this helps.