Welcome, I hope you like it here. I’d refuse and make it their problem. I’d accept using outlook dot com app or their encrypted messaging app on my locked down personal device.
If some chit goes down, they can try to compel you give them your phone for a HR, police, insurance claim, L&I investigation, or almost anything. Regardless of your involvement/actual culpability. If this moment ever arrives I’ll delete the company app, then reset the device and wipe all the data, then hand it over and immediately suspend service on the device, then replace it. This is just the device part. Good luck.