Your day off is a day off. Not a day “available if needed.”

Available if needed is not a day off, it is a shift where you happen to be at home. The phone stays within reach, the plans stay provisional, and nothing in you actually switches down. Most of the rest in a day off comes from being certain it will not be interrupted. That certainty is the thing worth protecting.

Before your next day off, say which hours you are not reachable, and then put the phone somewhere else. Not on silent in your pocket, somewhere else. One genuinely uninterrupted day beats three half ones.