Add External Audio to iPhone Video Recordings

Is there a way to do this:

I want to use my iPhone's camera to record videos at a live music event but instead of the audio coming from the room, I want to connect the output from the mixing desk to my phone so that the audio comes directly from the equipment (rather than the general sound of just being in the room) so it's best quality.

Is it possible to do this?

The mixing desk has stereo RCA outputs and my iPhone has the USB-C connector. I can find a splitter cable with stereo RCAs on one end and a USB-C on the other but will this actually work? I seems that this type of cable is used to take the iPhone's audio output and send it to external speakers (rather than an audio input from an external device).

Any help is much appreciated!