You know what's funny about this? The phone call quality of iPhones since the 6 series has been atrocious..
You know what else is funny? I’ve owned every single iPhone through multiple carriers throughout the years, and the iPhone 6 never posed any reception issues for two years of ownership. I’d say that you need to consider the carrier, LTE Signal/location, ect before you make any insinuations that it’s been atrocious.