I'll see your large text size and raise you larger text size.
As previously discussed, iOS 7 features Dynamic Text, which lets you across the entire device. The slider for Dynamic Text can be found via this path:
Settings > General > Text Size
If you have poor vision and find that the largest text size via the above setting still isn't legible, there is a way to increase its size even further. Head back to the General page in Settings and tap on Accessibility, which is directly below Text Size.
Next, tap Larger Type.
At the top of the next screen, tap the switch to turn on Larger Dynamic Type. When enabled, the slider below doubles in width, giving you twice the range of the slider on the Text Size menu.
As long as an app supports Dynamic Text, it will display text at your preferred size.
For more on Apple's latest mobile operating system, I will refer you to CNET How To's.
Apple - USE TAG
reading•How to make the systemwide text size even larger in iOS 7
Sep 19•iPhone 11, iPhone XI or iPhone Lemur?: Apple still has a 2019 iPhone naming problem
Sep 19•The Apple Watch Series 4 takes heart monitoring to next level
Sep 19•Photos shot on iPhone XS Max and iPhone XS
Sep 18•How to find a song by the lyrics with Apple HomePod