The paperback had a coffee ring on the cover that wasn't mine, left on a park bench by whoever had it before me, half a library due-date sticker still stuck to the spine from some branch I never identified. I read the first chapter standing at a bus stop and finished it a month later than I meant to.
Your first day
Read for fifteen minutes with your phone in another room, not just face-down nearby. Pick a book already sitting around, ideally under three hundred pages. Set a timer, on your phone before you move it or on a kitchen timer, and read at a normal pace until it goes off.
Most people leave the phone face-down on the same table, thinking that's enough. It isn't. Proximity alone can pull attention even with the screen off, which is why the fix has to be physical distance, not willpower.
The thing most people miss
Removing the phone from the room, not just from sight, fixed almost the entire problem within a week. I'd been convinced I had simply lost the ability to focus on books the way I used to as a kid, and that something about my attention span itself had permanently changed.
Once I stopped trying to build willpower against my own phone and started treating physical distance as the actual mechanism, moving it to another room before I even sat down, the reading itself stopped being the hard part.
What not to do
Don't push through the moment you catch yourself rereading the same paragraph twice. That's not a sign to concentrate harder, it's the signal to take a short break. Another few pages forced past that point rarely sticks anyway, and it just trains you to associate reading with fighting your own attention.
Forty minutes passed one evening before I checked, in a book I'd sat down with for what was supposed to be a quick session, because I hadn't set a timer that day and genuinely lost track. Reading two books at once, one fiction and one nonfiction, is worth trying next, since for a lot of people that's what keeps either one from stalling out half-finished.