Xert is designed as a dual device platform running a mobile phone app (or Connect IQ player) in conjunction with a browser page on PC/laptop/tablet (running Remote Player or Session Player).
While you could run the Connect IQ player alone, you will need to make your workout selection from the Training tab at xertonline.com before starting the player.
The EBC phone apps have many more features than the Connect IQ player which is limited by the Garmin platform.
I also use the Connect IQ app with a Garmin 530. I do not use the phone.
Be sure that you actually select the workout you want from the Training tab on the website before starting the Connect IQ app on the head unit. First, go to the Training tab, then find your workout, then click the select button for that workout, then make sure the workout is listed at the top of the page where it says Selected Workout: with a checkmark. I’m not sure if this is your issue, but if you do this before starting the Connect IQ app on your head unit, then the correct ride should load.
It can be confusing at first because the selected workout on the Training tab is not necessarily the same as the workout shown on your calendar under the Planner tab. You can’t just click the Automatically Create Recommended Workout button on the calendar and expect the ride to load on your Garmin.