iPhone 6 plus has bad audio quality on phone calls

I am having the same problem. I didnt have this problem for the first couple of months of use, but now it is really starting to get to me. I would pop in the sim to other phones I have for few days and I won't experience the same problem yet when I went to Apple Store they were claiming that it is the carrier. They said they did the tests and I dont know how accurate those tests are that did not find what what wrong, but I told them the problem is intermittent, and when it occurs, the other person can barely hear me. No dropped calls, just the quality can really deteriorate pretty badly. They were unable to help me and this really puts my decision in question if I should buy the next iPhone. Honestly, I prefer Android and the only reason keeping me to stay with Apple is their customer service but it does seem like over the years, it has been going downhill when it comes to support unfortunately.

I'm posting this to help some others if I can. I have Verizon as a carrier and had the I phone 4 and 5C and had no troubles. Recently I upgraded to the latest greatest I phone 6S Plus. I got so frustrated that I was going to return the phones and I love my I phones. I got three 6S plus and all three were doing the same thing. Poor call quality, dropped calls 90% of the time, my voice was going in and out to the other people I called and they kept saying hello, hello and someone would call and it would ring once and disconnect. Also I would send texts and they would say delivered and the recipient would not get the text.I brought them to the Apple store and they ran diagnostics and they came up good. So here's what I found out and it's 100% the answer because it worked on all my phones and they're good now. One of the new features Verizon had launched was making the I phone capable on their network for HD Voice and being able to do two things at once like talk on the phone and search the internet. For the I phone this started with the 6 and above. The feature is called LTE. So what Verizon told me was that at this point they are working on the LTE towers being able to switch off or hand off to a 4G tower. Also they are working on Wi Fi calling being able to switch off to LTE towers or 4G towers. So right now that's a problem. The 4 and 5C worked on CDMA networks. The LTE network is not 100% yet so if your on a call and you are connected to an LTE tower and the phone switches to a 4G tower your call will become poor or get dropped. Same thing goes for Wi Fi switching. None of this will work mind you if you get connected to a 1X tower. So the answer is go into settings/cellular/cellular data options and under enable LTE put the setting to data only. This will keep the phone on the CDMA network and you will have no more call issues. The down side is that on CDMA your phone will do only one thing at a time. Not a deal breaker for me because that's the way my old I phones worked and I was ok with that. The good news is that once they iron out the bugs you will be able to turn LTE back to voice and data and have the phone capable of doing two things at once. They stated they currently are working on the issue and it shouldn't be to much longer until it's set. Now when XLTE becomes available which should be much faster any phones that are XLTE capapble will work and shouldn't have any switching or hand off issues. XLTE is NOT released yet by Verizon. I'm assuming if you have another carrier the voice and data setting will also apply to them if they are also having hand off or switching issues as well. So I hope this saves someone who reads this a lot of frustration and exchanging phones only to get the same results ! Again in short put LTE to data only until they fix their issues.

I Think you may be experiencing #volumegate

iPhone 6 Plus Volume