Put it in airplane mode, this will switch off wifi, bluetooth, and data connection. I keep it off all of the time on the tablet. If I need to use my mobile I ALWAYS put it in airplane mode. No chance of interference that way. I’m guessing the DND wont actually switch these off?
The “notifications” you want to get in the FlyApp are “within the app” … not typical phone notifications (calendar, twitter, etc that appear at the top of the phone screen), so you probably don’t need to exclude the app from DND.
Nothing beats keeping an old phone as a stripped back drone-phone with the bare essentials installed only. (No SIM either, in my case.)
@Bilbo Just 1 thing to remember, if you get permission to fly within a FRZ then you need to keep your phone active in case the relevant ATC need to contact you.