When I take a day off (only one day), I don't usually switch off, unless I'm busy and can't answer the phone. I usually ignore emails until the evening.
I mostly use that free day to finish some private obligations, I rarely lie down and rest all day.
But when I go on a summer vacation or some city tour abroad, my work phone goes into Airplane mode. That is the advantage of carrying two phones (a private one in addition to an official one, because you can easily divide the time... Hm, this is worth writing a post about 🙂).