Hi CharlesRatty,
Welcome to thew Apple Community.
We are all Apple users, like yourself.
Re: Does anyone know why my voice isn’t being picked up by my microphone?
Sorry I don't know why, could be any one of various reasons.
Wondering which app you are recording with when the difficulty occurs.
Apple support have articles online (links below) that may help "troubleshoot"
Eg: "Control access to hardware features on iPhone":
Says:
Review or change access to the camera, microphone, and other hardware features
(ie: Seems you can turn access on or off for apps.)
Control access to hardware features on iPhone – Apple Support
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Get help with the microphones on your iPhone, iPad, and iPod touch:
If the sound is unclear during phone calls, during FaceTime calls, in video recordings, or in apps, learn what to do
If the microphones on your iPhone aren't working - Apple Support
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How to change microphone and camera modes in FaceTime on iPhone and iPad:
https://www.youtube.com/watch?v=XIzzAR7S-7Q
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If you have issues with sound quality:
If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support
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Adjust the audio settings on iPhone - Apple Support
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If needed, you could get help and support from Apple:
Official Apple Support
All the best :-)