What is the issue?
This report shows pages where 40% or more of the text has a font size smaller than 12px, which is too small to read on mobile devices. Font sizes smaller than 12px may require users to zoom in to display text at a comfortable reading size which has a negative impact on usability of your mobile website.
How to fix it
You can fix this issue by checking your font sizes in your CSS. Aim to have a font size of at least 12 px on at least 60% of the text on your page. If you’re not able to change font sizes, download the list of URLs and pass them on to your developer.
The URLs are sorted according to OPR (number of internal links a page has), but you can also sort or filter according to Google Analytics data to more easily identify your high-priority pages.
Learn more in this article.