My I-phone 6 plus no longer lets to make phone calls nor receive them. When I was able to talk on the phone I couldn't hear very well despite the fact that my volume was turned all the way up. Any suggestions?

The geniuses at the Apple University Village have excellent diagnostics in. If it is just advice you need on the spot, the will give it free. If there is a hardware or software needed they will will let you know cost if the device is not under warranty.

Hm. Phone not able to make or receive call... but when you were able to talk on it.. That's conflicting diagnostics. Sounds like sporadic episodes of something. I used to also have issues hearing the phone conversations even with the volume all the way up, but after I cleaned out my earwax, I was able to hear clearly. Still poor signal issues, tho. That's a separate issue.

Take it to the store they will fix it

Apple store will diagnose your phone and tell you what's wrong and your best options.

Bring it into the store.