Above is a mic jack going into a pre-amp. As you see the tip of the jack and the ring of the jack are both connected to the plus side of the electret microphone.
And when plugged in, it seems like the tip of the jack is coupled to the blocking cap of the pre-amp. And the ring of the jack establishes the connection for supplying biasing voltage for the mic through 2k resistor.
So as we can see the electret microphone's positive terminal needs two junctions to be coupled to two different points at the preamp side. There is two segments here: the tip and the ring.
But how about the connections in the case for a TRRS jack and a preamplifier? There is only one segment spared for the mic in a TRRS jack. How does biasing and AC coupling works in that case? I couldn't find any illustration or circuitry similar to the one I provided above.