Oh, this is a familiar topic! I had a similar situation when I needed to show a presentation to a client. Everything was solved when I found one app that allows you to transmit the image more stably. There they also suggested how to use the app to cast iPad to Roku, and this really improved the broadcast. By the way, if the Internet speed is good, then everything works like clockwork. Have you tried turning on the “Do not disturb” mode on your iPhone so that notifications do not interfere?