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

I'm trying to upload a professionally recorded voicemail greeting, but can't find the right combination of connectors. I want to specifically upload my recording, and thought I could play from PC directly to the phone using TRS to TRRS adaptor (with a, but I'm not getting signal. Does the adapter not send the stereo to the mic channel? 

What's the solution?
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.