Practical
The advice you'll usually find is some version of "just leave it in another room" — true, and about as useful as being told to "just eat less." Correct, and almost nobody manages it, because it depends on remembering a decision at the exact moment you're least equipped to remember anything.
Habits don't break because you want them to. They break when the environment stops supporting them. Willpower is a limited, depletable resource. Environment design works every time, because it doesn't ask anything of you in the moment.
In practice, that means the fix isn't a rule you enforce on yourself, it's a physical setup that makes the old behaviour slightly harder and the new one the default. A phone left on your bed in the next room still involves a choice, every time. A phone with a specific, designated spot right at the bathroom door — the one you pass through automatically — removes the choice almost entirely, because putting it there becomes as automatic as the reach used to be.
This is also why phone lockboxes with timers tend to get abandoned within a fortnight: they add friction (a code, a countdown, a small performance) exactly where you want to remove it. The goal isn't to make the phone hard to retrieve. It's to make leaving it behind the effortless option.
If you want to test this without spending anything: for one week, put your phone in the same spot outside the bathroom door, every time, no exceptions. Most people notice within a few days that reaching for it becomes noticeably less automatic — not because they've developed discipline, but because the object simply isn't where the habit expects it to be.
And that's why I urge you, for the sake of the human race and your own follow-through, to consider any product that removes the decision entirely rather than asking you to make a better one each time. We happen to make one — drop it. It's a box. It's outside the door. That's the entire mechanism.