I guess your using the mixer for headphone cues, remote control of levels? otherwise what purpose is it serving? If possible eliminate it. if not for all, for as many as possible. Plug the mikes directly into the snake, Then, and only then would you activate the Phantom power of the interface. The mixer will just add extra noise to the signal path..grounding issues etc.
The interface will have Phantom power for the XLR mike inputs. The mixer, if you use it, should be patched into the Line ins on the back which will not have phantom power anyhow.