Thanks, the Onkyo DP-X1 isn’t a phone and must not have the same settings. However, I figured it out.
To get the DAP to act as a Roon endpoint, you have to download and use the Roon Remote Android app on the DAP. Then in the Roon app, go into Audio setup, find the Onkyo as a connected device, configure its settings, name it, and save it. You can then select the DAP as a Roon Zone in the Roon Remote app and stream to it just like any other Roon Zone, via the Roon Remote/Controller. This gives you access to your stored library of music and Tidal.
You then have the option of listening to Roon in 1 of 3 ways: 1) from one of the two headphone outputs on the Onkyo, 2) if you select line output and connect a 3.5mm to RCA stereo cable to an amp, preamp, or integrated you can listen to the analog output from the Onkyo on your main system, or 3) you can use a USB OTG cable to feed a digital stream to an outboard DAC which can then analog output to any system of your choice.
This is basically what Ged was showing in his screen shots a couple of days ago but it took me a while to figure out how to do it. Duh!