If your iOS device has its microphone sensitivity too low or too high, adjust its settings so your voice will sound clear on the final recorded track.
The physical volume buttons on an iOS device control both the audio output (speaker volume) and the audio input (mic sensitivity).
Step by step:
Open the device's Settings.
Scroll to and tap Sounds.
Turn on Change with Buttons.
On the side of the device, push and hold the physical plus button (volume up).
The device's microphone sensitivity is raised.
A Host or Producer can adjust a participant's output volume to balance the sound during the live call, but this does not change the audio signal that is recorded.