The iPhone OTG camera adapter gets the SR3D USB devices to plug into your iPhone, enabling most USB microphones and USB mixers top work with your iPhone.
You may require to plug in an external power source to the lightning adapter so that enough power can be used by some USB microphones, using a standard lightning charging lead. All SR3D USB microphones and SR3D Basic mics using the USB adapter in our shop do not need external power, as the phone is powerful enough for this.