Xiaomi phones (not sure about others) allow you to have two separate "spaces". Not sure how it works under the hood, but it's basically like rebooting into another Android instance - even the Google account is not shared, apps are not shared, nothing. You can switch between these spaces from lock screen simply by entering a correct password for the one you want, you can configure what notifications and when can "bubble up" to the primary space, etc. It's an awesome feature.

My employer provides a work phone and subscription, and I am free to use it privately. I've chosen to keep that phone work-only, so I have bought my own private phone+subscription, and never the twain shall meet.

The work phone gets left in a locker at work along with my work laptop, I refuse to bring it home with me until I have agreed in advance to work from home for some specific task. I know a lot of employers expect their employees to be available at odd hours, but I refuse to participate in that.

I made this decision after suffering under a boss who would call and email at 22:00 and expect results to be ready on his table next morning by 8:00.

Only a very select trusted few of my colleagues have my private phone number, and they will only ever use it in a dire emergency.

Are you not friends with any work colleagues who would want to call or text you as friends?

No, not really. I do have some "favorite colleagues" who I enjoy working with and chatting about this and that over lunch, but they're colleagues, not friends.

My circle of friends is entirely separate from work, there is no overlap, which is just fine by me. I prefer keeping work and my personal life separate.

When I start at a company I bring my own phone and own data plan. The dev team gets my phone number and nobody else. No work email on my phone, only the work calendar so I know how early to start the day.

That way you don't have to carry two phones, be tied to a dual-sim phone or have troubles when you leave the company (in case you use the company phone number for private calls too).

Does accepting the employer's phone mean you are required to have work email on your phone, it's not just for phone calls?