Elgato Prompter + iPhone

@Thomas Umstattd Jr. said in https://www.authormedia.com/adapting-a-podcast-to-youtube that

“Instead of giving your old iPhone to your kids, let them enjoy a phone-free childhood a little longer. Permanently install it in your Elgato Prompter setup, and you’ll have a solid video solution.”

I have the prompter and the iphone jack—But I can’t figure out how to have this work with a microphone. How do I configure the sound?