“Don't check your phone” just leaves your hand empty, and an empty hand eventually finds the phone anyway. The real fix isn't banning the phone, it's deciding ahead of time what your hand does in that first five minutes.
What works for me is putting on a sound before I even drink water. Something steady playing while I open the curtains or make coffee cuts the urge to reach for the phone by a lot.
It's a small detail, but it works, because instead of setting a rule, you're just redirecting the habit itself.