The idea is simple. Or at least I think this idea could make a difference. If we want people to use their phone for perhaps reading and improving their skills in mathematics for instance. Then the release format for the Open Source Textbooks need to be more mobile friendly.
One way this could be done is if the Open Source Textbooks are released in an adaptable screen size HTML version. Besides residing on the web you can convert these HTML books to apps using some web to app software. Then they would become accessible offline.
Since a lot of books would still be in PDF version. I wonder if the PDF reader could adapt and render the text to fit the mobile screen. One way this could work is if the software recognizes the text area of interest after pressing on the text and reshapes it to be mobile friendly for zooming. The difference is that you would only need to scroll up and down. Not also sideways which makes the experience not very pleasant.