Say you want to quit sugar or smoking. Would you still buy cigarettes or chocolate and carry it around in your pocket everywhere you go because you should rely on willpower to beat the addiction? Very few people do that because you become vulnerable when your willpower is at it's weakest.

Usually it works better to exercise willpower to constrain your future self's available actions. For example, by not buying chocolate or cigarettes when you are at the store.

The same principle applies to your phone. Use your willpower to constrain what your future self can do with it.