Record audio in iMovie on iPhone
You can record audio, such as voiceovers, directly into your movie project.
Recorded audio clips are colored purple in the timeline and can be edited in the same way as any other audio clip.
In the iMovie app
on your iPhone, open a movie project.Scroll the timeline so that the playhead (the white vertical line) appears where you want the recording to begin.
Tap the Add Media button
, then tap Voiceover 
.When you’re ready, tap Record.
After a 3-second countdown, recording begins.
To stop recording, tap Stop.
Do one of the following:
Delete the recording and dismiss the recording controls: Tap Cancel.
Start the countdown again and record a new audio clip: Tap Retake.
Listen to the recording: Tap Review.
Keep the recording and add it to your project: Tap Accept.
After you record audio, it becomes available in the media browser (in Audio > My Music > Recordings) so that you can use it in another project.