iPhone 7 sound quality poor since 10.3.1 update

I have an iPhone 7. Since the most recent (10.3.1) update, my in-call sound quality is poor and phone volume is low. Note that this issue only applies to the earpiece and not the built-in speaker.

I have had the phone for 6 months, and had no issue prior to the update.

I have rebooted the phone, backed up and reset the phone and neither had helped.

Please advise if there is a solution to this issue that won't involve an appointment at the store.

Thank you.