Problem: You need to add 3 mics to a mixer, which only has one available channel.
Solution: Insert a ProMIX between the mics and the mixer. Each mic channel on the ProMIX has both phantom power and low-frequency cut selectable via DIP switches plus a level control. The balanced XLR line output can be connected to a mic input on the mixer and headphones or a powered monitor can be connected to the Phone/Aux output. And if AC power is not available, the ProMIX runs on batteries as well.