You’ll need a TRRS 3.5mm break out plug and cable, phone inputs use an an extra ring
on the plug for audio in, it the first ring on the plug.
Old VCA camcorders used the same plug, if you get one of those the audio input is the
yellow plug that was used for the video.
You will also need to attenuate the audio signal from the mixer line level out down to mic level and maybe need to use transformer isolation between the two.
Or…. get an audio input interface that would plug into the the USB jack on the phone, the kind used for the recording.
With an interface you may still need to get an inline attenuator as most of the interfaces are mic level input.