I was cramming for a noise show in the park a couple of counties over yesterday.
There's a lot to unpack here, and you'll have to forgive me - but I'm resistant to immersing myself into a project that is geared toward being a saleable product without compensation of some sort. But here is my understanding of phantom power (I'm not looking shit up to confirm, so this may be factually incorrect).
At your mixer, the signal pins should both be DC hot. This is because you do not want to run DC voltage "down" a transformer in an unbalanced manner and cook it.
Where are these measurements taken? At the mixer/power supply, or some other instance of XLR?
Pin 3 is ground. Negative probe to pin 3 referencing any of the other two pins should read a positive voltage. I'm not seeing that there.
I'm not 100% clear where the unbalanced phone plug is coming into play. Generally speaking, you don't want DC across a phone plug.
I don't think it takes a lot of bias voltage to charge a carbon element. If you're dealing with vintage elements I'm assuming you've familiarized yourself a bit with their quirks.
https://www.tamuracorp.com/clientupload ... C-5017.pdf
Did that SINGLE PAGE .pdf take like a minute to load for anyone else? WTF?
Anyway, that is a 600:600 transformer. Transformers are rated at AC impedance, not DC resistance. The seller did not provide hardware under false pretences. That lower DC resistance called out on line 7 is why it is important that the DC fed into the circuit is balanced with respect to the iron, as transformers go funny really quick when you saturate the core.
Which brings me back to your DC readings and my misunderstanding of them.
FWIW, my eyeball take of the original circuit looked good. I still don't know where the XLR to TS is coming into play.