Comment by GFischer

I don't think you can stream iPhone's microphone from Safari with WebRTC.

The plugin I mentioned is http://skylink.io/plugin/ , but it only works for Safari on Mac.

You'll need to build a native app

https://webrtc.org/native-code/ios/

or try Bowser

http://www.openwebrtc.org/bowser/

(I haven't yet).