Hi! The width doesn't impact the size of the font used inside. If your selection contains multiple font sizes, the topmost font name of your selection is displayed. Changing text size in Phone Settings do not affect change in OneNote. Changing the default font style, size, and color is done in a different way than other Microsoft Office applications like Word.
Highlight selected … You can change the default line spacing by following the steps below. Click on Options, This will open OneNote Options. I agree that it is pretty small in windows 10 mobile version. This is what you use to navigate the OneNote document and change font color, size, add multimedia.etc. Microsoft's OneNote app for Windows 10 will now allow the editing of attached files. The change will reflect in the OneNote app.
The reason I use a custom style sheet is because it limits the fix to Internet Explorer 11 and does not affect the News App or the Health & Fitness App. You can save articles with the Microsoft OneNote Web Clipper extension to organize your web-based research more efficiently. But if you don’t like the default Calibri font and want to set a different font as the default font writing emails, you can do so under settings. You can print a page, section, or notebook from Microsoft OneNote on a PC or Mac, though the process is slightly different for each operating system.