Go to your phone homescreen and look at the app dock (the bottom row that contains some apps and stays the same when you switch pages).
Which are yours? Any FOSS apps?
In my case, they are FDroid, Signal, Threema, Firefox and the defaul Samsung camera app. So, 80% FOSS…
Yep, all except for two: Crumpet and our Bank app. We can be pretty sure of this as we run CalyxOS and we have too many apps to list otherwise as everything on our ‘dock’ is in folders.