My new Android Phone is 3.5″ which is small enough to fit into my hand. But the fonts are too small to read, even I have choose the Extra large font size in Settings→Display or Large text in Settings→Accessibility. If you have the same problem, you shall try Big Font!
Enable Big Font
It is easy. Launch Big Font, choose font size, confirm update, and reboot your Android. If you upgrade to paid version, you will have more flexibility to change font size.
I capture pictures for most common apps in Android Phone. From left to right is normal, extra large in Settings, and 130% with Big Font. It shall help you to compare the difference.
Most programs are fine with Big Font. But some apps using fix size, they look a little weird on screen. Usually they will have the same problem with build-in large or extra large font size.