What frame rate is used by iPhone in "30fps" mode? I know in the Settings app, it says 30 fps.  But after importing the video files to a computer, QuickTime 7 and X both identify it as 29.98 [sic].  MediaInfo calls it as 29.97.  DaVinci Resolve calls it 30.00.  Which is correct, and is it drop-frame or non-drop?
30 frames per second is based on NTSC broadcasting standards that go all the way back to the invention of television.  All recording equipment conforms to this spec even though we don't use analog anymore.

NTSC actually runs at 29.975 frames per second, so both your apps are technically correct.  We just say "30fps" because it's easier to say and write than 29.975.