I have not seen any memtion of Plex yet.
If you copy your music from the phone to your PC or NAS box and then make one if those into a Plex server, Echo can be made to connect to it.
"Alexa tell Plex to play artist Chevala Vargas."
I have it working here at that level on my NAS box. I assume the same thing can be implemented on any Windows PC.
OTOH, I have not worked out the various command syntaxes yet, but it's there and I don't have to run down my phone's battery Bluetoothing to the Echo.