My approach on this problem was first to use the dedicated Apple's solution, that is the time management control panel. Spoiler, that never worked as I would turn on and off the constraints based on my needs. I was consistently unsatisfied and endlessly blaming my lack of will. Thus, I really understand the point of view of the author to readily constraint himself with the hardware instead of software knobs easy to turn off.

Rather of buying a new phone, it worked for me to just live with my iPhone 6 until today. It became so slow that it achieves pretty much the same behavioral perks but still supports a wider range of useful features imho like keeping my Spotify account usable on my commute. Opposidely, my reddit addiction -- and news sites in general -- completely disappeared as the website now takes seconds to load and the panel advocating to download the app takes up half the screen making it just unusable.