Hi @DrAnalyzer,
As others have mentioned here, the Devialet Phantom Golds are not Roon Ready, and I can’t comment on when, or if they will be, so you will need to use some kind of bridge device for the time being.
Using Toslink is one avenue to explore (you can find a few mentioned in this thread or use a Chromecast Audio), and it should also theoretically be possible to use a Sonore UPnP Bridge to facilitate the connection.
Note, I have not tested any of the Toslink adapters nor the UPnP bridge so please research this area further before purchasing to ensure compatibility with your phantoms.