I’m currently working on a Bluetooth Entrypoint, this will provide an easy way to make the Spotify to Roon connection. It runs on a Raspberry Pi and advertises itself as a Bluetooth speaker. You connect your phone to it like you do with any other Bluetooth speaker:
In the Entrypoint Settings you select the phone that has to be the playback device:
Then you connect to the Entrypoint radio stream in Roon and play it in the zones of your liking.
When this is available it will be announced in the Entrypoints thread you already linked to.