Unfortunately for this thread, I don’t do Insta so I wont be able to hear the recording.
This started out sounding like “the DN & DT output is too quiet” (because of the DI box suggestion). We’ve shifted it a bit to “the mixer USB output is too quiet”. Let’s dig into this.
Do you need to add as much gain to the other instruments? Do you use a DI box with those?
If the board has level meters on each channel, what level is the loudest instrument? What level is the overall mix (on the mixer, not the recording at the iPhone)?
Have you used the mixer as an interface to a desktop/laptop and run DAW software? Does the loudness issue show up there? Could you use a DAW to inspect level meters better than the hardware only solution?
Next level debugging:
Bear in mind that 0db on analog and digital equipment is different, that digital gear has to pay attention to the fact it will clip at max, where analog will “only” distort. So they’re made differently, use different scales. It often doesn’t appear to be the case because visual scales are made to look similar for convenience. If you can, calibrate your signal flows, or your expectations (i.e. get a db meter and measure stuff. It’ll get fiddly. Personally, I have struggled to commit to memory the differences between the scales (and I took a long break from music and mixing and have gotten rusty).