I got the same variety of bizarre responses from command using Voice Control. Think I'll take a vacuum cleaner to the front mic of my iPhone 6, which is on top of the screen right behind the left side of the speaker slit.
I do not believe it is a hardware problem with the front mic because it works fine with some features and not others.
There seems to be many who THINK they found a solution because some specific adjustment worked for them, however, I think that means there can be several causes from installation and app conflicts so one solution doesn't fit all.
One-hoop, who seemed to have the same problem we are said he solved it by resetting all settings (Settings>General>Reset>Reset All Settings) in message https://discussions.apple.com/thread/6765123?start=45
I don't know whether he then reloaded each third party app from scratch or not. It would seem he would have to to avoid recreating the problem by reloading potentially conflicting setting from has backup file. I'll send him a pm to find out.
Here is what I've ascertained by testing so far.
Hypotheses
Different functions activate different mics
1. Siri activates the front mic.
2. Dictation activates the front mic.
3. Selfie video only activates the front mic. Forward video activates the back mic
4. An voice iMessage and dictation activates the front mic.
5. Speaker phone calls, FaceTime, Skype, Hangouts, WhatsApp, etc., activate the front mic.
6. Voice Memos seems to activate all three mics. It works well when recording a selfie comment or recording audio nearby, even with iPhone lying on a table on its front or back.
7. Flipping the video cam from front to back seems to flip the mic as well.
8. Bluetooth connection with other devices blocks all three iPhone mics.
What Voice Recording Works for Me
- Speaker phone calls,
- FaceTime,
- Skype, Hangouts, WhatsApp
- Forward facing videos recording
- All audio recording features on all apps when using headset mic.
What Voice Recording Does Not Work
- Siri
- Dictation
- Voice iMessage
- Selfie videos