I use the Focusrite Scarlett 2i2 and my iphone 11pro. It works awesome, but it took a lot of research to get the right cables I needed to make it happen. I use a PC so I have the 2i2 connected via USB.
2. I use this splitter that goes to the L and R at the back of the 2i2
3. I connect the microphone end of this TRS splitter to the one in the pic above and the other end goes into my iphone via the little dongle adapter (since my phone doesn’t have a headphone jack input)
I hope that makes sense LOL. If you have any questions, you can PM me. It looks more confusing than it is, but it works perfect. Sound comes directly from the 2i2 into my phone and is crystal clear. You might need to adjust the settings on the 2i2 to get it how you want, but that’s how I do it.