Not easy indeed. I'd suggest switching the phone and computer off for the time of reading, but then maybe you are reading on the phone or computer, so it's extremely challenging to just read and not get distracted.

It helps if you are orderly in general: Anything you do, do according to plan, and have roughly the same plan for every day/week. And this includes the mind: Pay attention to what you are thinking, never leave important thoughts unfinished; while trying to finish a thought, think only what's relevant to that thought. Consequently: When you read, have an assigned time span for it, do nothing else during that time span, jot notes to help with comprehension of the current text, refuse interruptors and intruders.