The microphone isn't powered, so there's no way to do something as direct as you're asking for. A light indicating that it's "listening" would necessarily have to be controlled by software at some level.
This makes a lot of sense as mobile phones are an extremely hostile RF environment. If it were any other way, the phone's sound inputs would be flooded with that iconic "cell phone interference" sound.
Old but still interesting:
https://www.ifixit.com/Teardown/iPhone+4+Microphone+Teardown...
What you describe as "no way" is a 2-second napkin sketch for any witting electronics hobbyist, let alone a proper design EE professional.