You don't need to have your work communication on your private phone. If you want to do that, you can still temporarily disconnect them before leaving for holidays...
That statement makes a few assumptions. I don't have more than one device for this stuff. My business and clients all emergency numbers (which would include that person number if it existed). I also have a painfully small amount of self control and have in the past nipped off to check my emails for "10 minutes".
A holiday can be a good opportunity to disconnect completely.
I didn't the last time I went on vacation in Europe. My cell phone carrier also is atrocious and charges usurious international roaming charges, so that was a contributing factor, but it's really nice to unplug and go off the grid on vacation. You just have to do things the old fashioned way - print out your reservations and itinerary, get some maps.
20? I recall going to Europe for two weeks in 2006 (BMW European Delivery). Didn't bother bringing my dumb-phone. Just had a camera. I drove 2000 miles around Western Europe, 6 countries, had zero hotel reservations before I left, and had no problems whatsoever. This was in April so just popping into a hotel and finding a vacancy was not a problem.
When I go on holiday, I don't want business calls and emails following me. If I need to make a call, I'm sure I'll find a way to make it.