+48 volt Phantom power from 6.8K current limiting resistors (inside the deck) appears at pins 2 & 3, with pin 2 being the + (non-inverted) signal input polarity.
What this circuit is doing is clamping the voltage for the mic at a safe level, coupling the audio signal through the C2 in-series cap going to pin 3.
The resistors along with the C3/4 capacitors to pin 1 common are being used shunt audio signal out of the - (inverting) pin 3 input and make it a 'floating DC' signal common, but with no actual audio signal going to that pin. So the deck sees only the mic signal at pin 2, and pin 3 sees only a filtered no audio DC - input reference level.