Hi jimfetter
Muffled earpiece speakers are almost always caused by dirt/dust getting jammed into the mesh which covers the speaker at the top of your phone. You should try to clean this out with these steps:
# Apply tape to the area and peel it off a few times to remove large pieces on the surface
# Use a small brush (toothbrush works well) and a small amount of 99% isopropyl alcohol to scrub the mesh clean
If these steps do not fix your issue, you may need to open the device to clean out that area from the inside.
Best of luck!