The only way to really disconnect is not to bring the internet with you.
The remote possibility of checking one more time for updates is irresistible. But you can fight it by going for a walk with your phone, by uninstalling the apps that most call your attention, with the Do Not Disturb mode, or simply going Airplane Mode.
The more time you spend without these notifications, the less your brain will be expecting them throughout your day.
Let more "I left the phone at home" moments happen.