Right, step 1 -> get page images, step 2 -> author images into book file. While OCR is obviously useful for search, a rotated phone screen will let you comfortably read a pdf book just fine unless you are talking about something like a textbook, in which case you probably wanted a tablet anyway.

I wrote up a guide on the authoring process using FOSS tools for some Digital Humanities folks a couple years ago: https://github.com/wikey/bookscan

It gives some background on the problem and covers a Scantailor (page crop, rotate, deskew), pdfbeads (compression, book metadata) authoring workflow, with pdftk for some general odds and ends.