iphone 7 plus

[ANNPOW2]

I went in knowing that I wanted a iphone , I was gonna go with the 8 plus, but the sales man talked me out of it stating that the price wasn't really worth the difference between phones and the fact that the 8 plus is glass turned me off. I was happy with phone for the first month or two, but now I can barley hear teh person on the other line the call sounds muffled, low and like they are speaking to me on speaker phone . should I trade up ? or do you think there is a defect ? the phone doesn't have a scratch an has been in either a Otter Box or LIFE PROOF. I am fed up