|May 8th, 2021
An Android phone (likely iPhone too, but I don't know those) can record audio from any standard ("class compliant") USB audio interface. This may bring up images of spending hundreds of dollars on professional audio equipment, but if you only need a single channel and don't need a preamp (or you already have mixing equipment) you can use a "USB soundcard":
This is a Sabrent USB-C adapter one I got for $7.30 shipped.
This is "Settings > Video settings > Audio source > External mic (if present)", and worked without issue. Here's an example:
Videography courtesy of Lily
I previously made a lot of recordings with the microphone on the camera just because it was so much more convenient than combining audio and video from two sources, but I think I'm done with that.