My routine has just enough exercises that I don't always remember the reps / timing / order / proper form, so the phone serves as my reference medium. Understood and agreed though - it's ripe for distraction. I should probably just write the routine down.
I think it depends on the type of workout. I do a powerlifting style program that has a 3 minute rest time between sets, so I like to read during them.
If I were doing cardio or a circuit style workout I would forgo my phone and concentrate on the workout.