IPhone users cannot change the fonts used throughout iOS. The only system-wide changes available are font size. However, you are able to change the fonts used in some native apps and in Apple-made app purchases, such as the iWork suite. Font alterations can make reading easier, especially if you prefer specific serif or sans-serif typefaces while reading digital books or video captions. Different fonts can also be used in apps like iWork for iOS to customize the look of documents composed on your iPhone.
Launch iBooks and open an ePub or iBooks formatted file.
Tap the "Font" icon, which looks like two capital "A" letters.
Select a font from one of the seven supported fonts: Athelas, Charter, Georgia, Iowan, Palatino, Seravek, and Times New Roman.
Open the Settings menu, choose "Accessibility" and select "Subtitles and Captioning."
Tap "Style" and "Create New Style." From here, you are able to choose a new font, size, and font color.
Tap "Add font" if you don't see your ideal font listed in the "Style" window. This list allows you to choose from dozens of new fonts.
System-Wide Font Sizing
Open the "Settings" menu, tap "General" and choose "Accessibility."
Tap "Larger Text" and switch on "Larger Accessibility Sizes."
Move the font size slider until the preview text is displayed at your preferred size.