Textbook preaching occurs when a teacher (usually a supply/cover teacher who is relatively inexperienced) teaches pupils by relying solely on the contents of whichever textbook relates to her current lesson (e.g. a teacher covering in Chemistry reading verbatim from a chemistry textbook)
More often than not, this method does absolutely nothing to help students learn, other than reinforcing already-negative attitudes about supply teachers and forcing pupils to seek out their own means of learning.
The only exceptions include teachers assigning tasks from the textbook or simply asking students to read extracts.

the thing that you don’t have when you’re phones percentage is over 20