I can confirm this too. I went to Apple. They said diagnosis was fine including microphone. They gave me new SIM card & told me if that didn’t work to reset to factory settings & start all over again. Finally called Apple again today, frustrated I told them I needed a replacement. I paid $1,100 on a phone that no one can hear me on. This is an iPhone X, I didn’t have this problem with my old 6 plus. This is unacceptable Apple.
People tell me I sound muffled & connection comes in & out. The best phones were the 6 series. I shouldn’t have gotten iPhone X. I’m disappointed in Apple.
They need to come up with software or replacement phone.