Make Sure Your Speakers Are Clean
Dirty or blocked speakers and mics will absolutely ruin your call, and if you don’t take voice calls very often, you may not have noticed if the small speaker/mic openings have gotten dirty. So if your calls have taken a sudden turn for the worst, check on the upper and lower speaker sets to make sure there’s no grime, or dirt, creating problems. Carefully clean and remove dirt if it’s a problem – or take your phone into an Apple Store for a closer look if necessary.