Hello, I have the same problem - updated my IPhone7Plus from 13.1.2 to 13.1.3 - and since then the microphone and all the apps that use it (phone calls, Siri, voice memos, face time ...) are not working anymore. I have contacted Apple Support several times and visited the Apple Store - unfortunately without success.
A hard reset including a new IOS installation did not help. The only solution is the paid repair.
Unfortunately, Apple Support did not meet me. Last year (IOS 11.3), iPhone7 devices with audio errors were replaced with goodwill, but that was a one-time action to investigate the cause.
This was that an existing hardware defect could possibly be detected during an update, and after the update, this component might no longer work. What I do not understand is that the supposedly existing defect was not shown before the update and the microphone had worked fine. Now I have to use a BlueTooth Headset for my phone calls...
Would be happy about other experiences.