Is the loudness in connection to how loud it makes a noise when you recieve a call or notification or is it the loudness of a person's voice when in a call @Christie8 ?
When you play music through the stereo speakers how does that sound ?
There are diagnostic tool tests via your Samsung Members App and via launching the phone app and dialing *#0*#
Is dolby turned on in your settings ?
Settings, Sounds and Vibration, sounds quality and effects.
There is also other sound settings in this section.
When you press the volume rocker on the side of the phone quickly tap on the 3 little dots on the top of the pop up volume and look at what all the sounds are set to and adjust them to suit.
Apologies if you've tried these already.
Check both the top speaker and bottom speaker for debris.
Also check the usb-c charing port too for debris via a torch.
Don't use an air can to blow out these kr you couod drive debris further into the phone.
You may need to visit again for a second opinion too.
I wish you all the best. 
