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?