It doesn't need an answer tonight
The phone outside the window
The window is a decision. The phone is where the decision gets tested at ten past nine, and this chapter is about arranging the phone so the decision doesn't have to be made again every evening.
The principle is that the buzz shouldn't reach you outside the window. Not that you should hear it and resist it, but that it shouldn't arrive. Every phone made in the last several years has a setting that silences notifications on a schedule, and most let you choose which apps are silenced and which people can still get through. Set the schedule to the window's edges. Put the work apps, mail, chat, whatever your workplace uses, in the silenced group. That's the whole of the configuration and it takes ten minutes.
Then the other door. Choose the one route that stays open, and I'd make it a phone call, because a call is harder to send idly and easier to notice. Tell the manager and the two or three people who might genuinely need you that the number rings through after six. Then leave it alone. If it rings at nine, it's the emergency, and you'll deal with it. If it never rings, which is what happens to most people, you've learned how many emergencies there really were.
The other door is what makes the closed window safe rather than reckless. Without it, you're relying on nothing going wrong. With it, you're relying on people using the phone when something does, which they will, because you told them to.
Some people prefer to check the inbox once, at a fixed time, rather than never. Fitz and colleagues' experiment in chapter 11 found that people whose notifications arrived in batches three times a day did better than people who got none, on mood, stress and a sense of control. If you're one of those, put a single look at eight in the evening inside the window, as its last act, and keep the phone silent after. A chosen look at a fixed time is a look you can stop. The point is that the phone doesn't get to choose.
Then there's where the phone sleeps. Not on the bedside table, face up, lighting the ceiling. Derks and Bakker's diary study of employees with work phones found that on evenings when people managed to detach and relax, the phone did less damage, and detaching is easier when the phone is in another room. Charge it in the kitchen. If it's your alarm, buy an alarm. This is the single change most people resist and the one they report the most from.
The objection is that the settings are fiddly and you'll get them wrong and miss something. You might, the first week. The other door catches what matters, and the rest waits, and by the second week the settings are set and you've stopped thinking about them.
The practical step is tonight. Schedule, silenced apps, the other door named, the phone in the kitchen.