OK, I found it. See the schematic.
Phantom power drives the hot and cold leads with +48 VDC, with 0 V on the shield. It’s important, form a theoretical viewpoint, to make sure that hot and cold are electrically identical. The intent is that any noise that a long circuit picks up will be impressed equally on the hot and cold leads, since they take the same path. At the mixer, or amplifier, or whatever, only the difference between the hot and cold leads gets amplified, so the common-mode noise is, again theoretically, eliminated. So, the circuit has to be symmetrical with respect to the hot and cold leads.
It also can’t draw more than a couple of milliamps without violating the rules.
The electret wants to see a lower voltage - like maybe 2 to 10 VDC - and a not-unreasonable resistance in series.
The resistors in the circuit reduce to an equivalent of a 6.7 VDC source with a series impedance of about 6K1. The voltage is typical for an electret; the impedance is probably a bit higher than is typically used. The voltage divider feeds the electret across the transformer, and the electret delivers AC to the high-impedance side of the transformer, and that puts the low-impedance signal on the hot and cold leads. The matching transformer does a couple of things: it matches the relatively high impedance of the electret circuit to the low-impedance audio system, and it converts the single-ended circuit of the electret to the balanced circuit of the audio system. In the schematic, the electret should be connected to the high-impedance side of the transformer.
As for packaging, the whole thing fit inside one of these:
http://www.shure.com/americas/products/accessories/microphones/microphone-problem-solvers/a95u-line-matching-transformer That was handy, since it had the right connector on each end, and a matching transformer already inside. Three resistors and a little capacitor fit inside with no trouble. I recall that it wasn’t particularly easy to get into the enclosure, and it was especially tricky to get in without damaging it too much. I definitely voided the warranty in the process. Later, when that item disappeared, I used a cheaper matching transformer, and I built yet another unit inside an unshielded plastic case - I didn’t expect much from that one, but it worked as well as the others. The whole thing didn’t seem to be terribly sensitive to the quality of the components.
Purists will hate this circuit, because there’s a galvanic connection across the matching transformer. In principle, I don’t like that either, but it worked very sweetly for me. I played it for years, in several venues and on several systems, and it always sounded fine and delivered adequate output. Beware, though - the electret, as you might expect, fed back like a banshee.
I recall that I spent a long time figuring all this out - a lot longer than the circuit merits, in retrospect. I recall that I got an unacceptable level of power frequency noise on the first try. I got rid of it by wrapping the electret in aluminum foil, laying the foil across the grounded wire that supported the capsule, and heat-shrinking them together. That eliminated audible noise. I don’t recall any other problems in construction.
Your mileage may vary. I might well have gotten lucky with the electret. I’m not sure that I had any right to expect it to perform as well as it did.