Even if you don't look at a notification, part of your brain still gets pulled in, that feeling of not knowing what just came in is the actual distraction. It happens even if you never touch the phone.
When I turned notifications off, I expected fewer interruptions. The real benefit came from somewhere else, the urge to check the screen dropped too, because I already knew nothing would be waiting there.
So turning off notifications doesn't just cut interruptions, it breaks the checking habit itself. Together, those two things make the actual difference.