Hey @steve_holloway – Roon requires a Core, as described here.
If you tell our support team a bit more about the Onkyo streamer (like the model number), you may be able to use your PC as the Core, streaming to the Onkyo, and controlled by your phone.
That said, we offer no-questions-asked refunds during the first 30 days, so depending on when you signed up, you probably have a little time to get this working.
Start by letting us know the model of the Onkyo, as well as the details described here.