I check the return code from the borg backup job and issue a notification to my phone via NTFY if there was a problem.
Please note that return code 1 (warning) will be issued if a file changes while borg is backing it up so it's very common if you backup log files for example. Which is why I only notify for code 2 or greater.
You can also do it the other way and simply issue a notification no matter what happened, and just list the return code as-is. This is probably better since you also get confirmation that the backup job is actually running.
They have your identity the moment you put the sim in the phone. The phone have unique identifiers that are recorded when sold.