A week of lectures does not leave much spare attention. If the phone is the thing filling the gaps, the fix is boring and it works.
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For seven days, check the screen-time number your phone already records. Note the two apps that take the most time, and the hour of the day they take it. That is the only audit worth doing. Counting every time you pick it up is a project of its own.
Put the phone in another room for one block of work a day. Fifty minutes is enough. The study room in the building is useful for this because the bed is not in it. At night, charge the phone outside the bedroom. Sleep is the part people skip, and it is the part that shows up in the next morning's lecture.
Group chats can stay. Mute the ones that are not about tomorrow's seminar. You can read them after the work block instead of during it.