When I was working, I, too, had to keep my personal and work systems as separate as I could, for a number of reasons.
My work day was pretty much during day shift on weekdays, so my personal Android smart phone calendar had very little on it for those hours. About the only time that I wanted to show duplicate appointments was when I had to leave work for a personal appointment, e.g., a doctor's visit. I needed to show that on my Outlook work calendar so that I (and anyone looking at my work calendar) would know that I will be out of the office at that time.
The only other "work thing" that I can think of that was on my smart phone was an encrypted set of passwords to my various work accounts (along with all of my personal ones) in an Android app.
For backup purposes, I regularly synced my personal data in various apps on my Android phone with my personal PC laptop. My work information was backed up automatically by whatever IT processes that my employer had in place on the network.
In spite of all of this "separateness," there was almost no duplication of information. In situations like this, I always like to cite the old saying: "A man with one watch knows what time it is; a man with two is never sure." So, each data record resided in only one place (that was backed up somewhere, via sync'ing or otherwise), but the whole set of data happened to reside in 2 places, namely work and personal devices.
I hope this helps.
Joe