How to change the text size on iPhone.
If you want to change the text size on your iPhone quickly, you can also use the Control Center. Here are the steps to follow:
Swipe down from the top right corner of the screen to open the Control Center.
Press and hold the Text Size button, which looks like a large "A" with a smaller "A" beside it.
Slide the Text Size button up or down to adjust the text size.
Release the button when you've found the text size you want.
That's it! The changes you've made will apply to most system apps and some third-party apps. Keep in mind that not all apps support Dynamic Type, so you may not see the changes in some apps.