When I got a new phone, I decided that I would only ever allow certain behaviors with it, and exclude all addictive behaviors. The trick: I kept my old phone, and allowed myself to continue my addictive phone behaviors, but only on my old phone. For my new phone, I've built a habit of reading books (via Kobo and Overdrive), and taking photos.
I also allow video chats, and basic messaging, and navigation. Everything else -- checking email, reading the news, browsing Facebook -- continues on my old phone. I've found that, over time, the addictive behaviors have lessened a lot. I still read the news on my old phone, but I often forget where it is, sometimes for a couple of days.
I think this has worked, because I've not tried to stop my addictive behaviors, which is an uphill battle. Instead, I've allowed them, while also building new (and better) habits on my new phone. I keep my new phone with me, and spend a lot of time reading on it, which I see as a good thing
I'll often spend 15 to 20 hours, or more, reading books on my phone. For me, that's great. I've done more reading (high quality reading) than ever before, since I've started this strategy. I'm hopeful that it will continue indefinitely, though there are no guarantees.
If I need to do something useful, or just lazy/addictive, I let myself do it, but on my old phone. I do sometimes enjoy, and benefit, from reading the news on my phone, or checking my email on my phone. I don't have to expend a lot of willpower preventing myself from doing this. I have to spend a little bit of willpower making sure it only happens on the old device. So far, this has been a very effective, and relatively easy strategy, and my addictive/wasteful phone use has gradually and consistently dropped to a very low level.
TLDR; Step 1: keep your phone as is, don't lockdown or brick it. Step 2: get a new phone, and choose the behaviors you want on it. Be strict about this. Step 3: allow the old bad habits to continue only on your old phone.