I have an iphone 8. When I make or receive a call the other party cannot hear me. What is wrong with my phone?

87% is good. Apple's iPhone User Guide says: "If your iPhone isn’t working as expected, you can try restarting it by turning it off, then turning it back on. If turning it off and on doesn’t fix the issue, try forcing it to restart.":

Turn iPhone on or off - Apple Support

õ¿õ¬

Pepperdawg ~ Does your iPhone 8 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

õ¿õ¬