Just to confirm, while using your phone regularly, the phone app keeps popping up, by this you mean dialpad?
By any chance are you tapping on a group of numbers that could be pulling up your dial app? What types of apps or things are you doing on your device, when the phone app randomly appears?
that is very odd, I am using an S10 and I have not encountered this issue.
When did this start happening? It seems like you have tried the basic troubleshooting steps.
Maybe check your settings in accessibility as well, and if all fails, you may need to try a factory reset but of course back everything up with Samsung Smart Switch