There evergrowing number of persons using smartphones to consume content encourages content providers to avail their material in ways for easy reading. Reading materials in standard A4 size on such phones require the reader to tilt the phone horizontally and possible to expand the text for it to be legible - all of which creates a cumbersome and awkward experience.
The solution proposed here is to use a word-processor, such as LibreOffice which permits the writer to create customized sized pages by which one would do the following:
Create Page Size w210 x ht360pts
Open tab: 'Format'->'Page-style'; With page layout at 'Right and Left', set 'Page Format' width to '210pts', height to '360pts' (a Portrait type orientation) with the margins (Left and Right) at '9pts' and top/bottom '5pts' respectively. Note: 14pts = 0.5cm
Print Page to PDF
Having saved the above page-size, one will note that the usual 12pts characters will read well on the smartphone once one save the completed work as a .pdf file.
Test the resulting PDF file Load the .pdf to a smartphone to view the result as a means to ensure that it is satisfactory.
Note:
Content that exceeds 50pages in this type of format will be harder to find specific pages - although the 'find/seach' tools in the usual PDF smartphone reader will be useful to get to key-words in such texts.