How to record from TRS PC out to TRRS Cellphone in?

Record??????
Just drag and drop.
Or just record with the phone mic.

Voicemail greeting can only be from a microphone recording, not an imported file. Recording a professionally-recorded greeting over the phone mic or external mic from a nearby broadcasting speaker is crap. I want to record digitally what the pc sound card is putting out.

I'm not 100% sure my current 3.5mm to USB C adapter is TRRS, so I'm getting a new one shipped. In the meantime, I'm ignorant as to how the wiring and mic input works in the TRRS to USB C adapter, thus the wiring question. Not sure if the adapter is meant to carry the stereo signal to the mic, or if it needs to be line, or what. Not my arena.