I don’t think a smart phone in your pocket all day with a GPS and microphone that you use as a central hub for all your communications, notes, research and appointments and so forth, can really be considered for its privacy - and it appears thru researching apps on these smartphones the authors have the same conclusion.
On the contrary. I don't have to consider the privacy implications of different paper notebooks - they all share a similar security profile being things that physical access is both required and sufficient for. For something like a smartphone, considering privacy implications of choices is vital.