the font size stays the same. If you want to bold the text and make it larger so it stands out, you can easily add the appropriate tags. How to Delete Large Amount of Old Posts on WordPress Blog.

But on the larger, high-definition screens that were introduced in later models, the fonts looked off. The bold letters were ... typeface’s appearance on a “big pile of devices,” ranging ...

You can't change the actual font on ... to make the text larger or smaller. If you have trouble seeing your iPhone's text even at larger sizes, you can also make all the text bold.