Hi BBF,
Great question. I've been using my COBI now for more than half a year. It came built in with my IZIP ProTour. I really love it. I will agree with Court though - the initial setup wasn't a great experience (based from his IZip ProTour review). Took me a few trial and error, but eventually got it going. So do keep this in mind.
To answer your question, the COBI will work in the background. I would suggest turning off the COBI navigation, in replacement to using Google. It will still track the amount of miles you've covered and provide you charging time on your ebike, as long as you do not close the App. I am using a Samsung Galaxy S9+ and it has worked great. I suggest keeping your phone plug-in the charging cradle. To this day, I have not notice a major draining from my ebike battery.
I've also used my COBI without my smartphone which is why I love it so much. Granted, I don't see the charging time left on the app, but I can check that from my bike battery. I can also change my speed from the handlebar switch, as well as use the built in electronic bell. I think, the best feature of COBI is the integrated lights with turn signal, and especially the built in alarm. I used the alarm all the time especially when I park my bike for more than an hour. I hope this helps (I've also attached photos here). Good luck to you.
Cheers!