Yes, harm reduction is possible, but it requires motivation to do so, I believe is one side of the argument presented in the comments around here.

The phone is maybe a bad example as something that can be removed in one swoop.

Picture a student (with no phone, they use their desktop computer in 2007) having an exam in 7 days and carefully planning on the first day - I'll have to get through 350 pages before this exam. 50 pages a day is more than easy mode. Then they start on the first batch and suddenly get the urge to clean their room. Once that's almost done, they start wondering if penguins actually have knees or not, so they go online and check. Then they see the book lying on the bed, 6 pages / 50 done. Get back to the book but realize they stopped in the middle of a long paragraph, time to go back to pages to remember what was said. 10 more pages. Maybe they should have some coffee. They suddenly have the urge to find out in detail how coffee is roasted. At this point some 4 hours have passed, the room still isn't fully clean, nobody knows for sure if penguins have knees and there's a bag of open coffee grounds lying somewhere in the dorm room. Where the hell was it? And they needed to pee for like 30 minutes now but how is coffee roasted?

Exam is coming and this shit has been going on for 3 days. The dread now sets in, with the needed amount of work doubled. Must avoid the dread. Brain goes back to old tricks and pulls a quick one to distract from dread.

2 days left - brain goes into oh shit mode. Dread-distract-repeat. All nighter time. Somehow it works.

I do agree with you that phones are attention-traps and would say that they make make it easier to mask this sort of behaviour by just staring at a screen, because the sheer amount of stuff you can do on your phone from browsing pictures of cats to finding actually interesting content (video or otherwise) to ordering food or cleaning supplies or chatting with friends means it's now easier than ever to get distracted while appearing outwardly otherwise unoccupied, but the brain is firing in random directions like a dog chasing s fleet of scared squirrels.

All this to say that yes, you can throw the phone away, but never underestimate the ability of a distraction-prone mind to keep itself distracted.