Below shows a dynamic microphone equivalent circuit:
As you see above, the microphone output is first converted to balanced circuit via the transformer. The signal then travels along the cable until the preamplifier. It seems the signal is splitted to bipolar by the transformer. Here is another example.
But how about in headset microphones such as this one? I guess they are also dynamic mic type. But obviously there is no transformer or another circuit after the headset mic. Does that mean the headset mics are single ended unbalanced transmission? By transmission I mean the cable from the headset mic to the TRRS jack which goes into the smartphone audio port.