@Waynet Hello, go to Samsung members/Assistance/Diagnostics and perform the speaker test. If the call speaker is still very low, it is likely that the device needs to be checked. maybe clear cache and data of the Phone app, if the problem is present only in phone calls.
If none of this helps, Reset all device settings/Settings/General management/Reset/. In none of these steps will you lose personal data, only settings and configurations will be affected. Greetings.
"The quieter you become-the more you are able to hear..."