Hello,
Since I have updated to beta 4 for iOS 11 I have been receiving an issue where the other person cannot always hear me. I always have service and multiple people have reported not being able to hear me or I sound like a robot. I didn't have this issue when I was on beta 3, but figured I would mention it on here just in case others think it may be just a coincidence. I did not drop my phone recently either. I am using an iPhone 7.