How to increase the text size in iOS 12 for iPhone/iPad/iPod Touch

1. Open the ‘Accessibility Settings’: Settings > General > Accessibility. (See the article Open Accessibility Preferences on this website for more information.)
2. Under the ‘Vision’ section, tap on ‘Larger Text’.
   
3. To access the full range of text size options, tap on the toggle switch to the right of Larger Accessibility Sizes.
   
4. To change the text size, drag the slider to the left or to the right.
   
5. Enabling ‘Larger Accessibility Text’ does not increase the size of the ‘title bar’ text at the top of the screen. However, if you long-press on the title bar, that text will be shown in a larger size in the centre of the screen. Note: To enable this feature, you need to set the  ‘Larger Accessibility Sizes’ above the 50% mark.
   
6. When you are happy with your settings, either tap ‘Back’ in the top left of the screen to return to the main ‘Accessibility’ settings screen or press your device’s ‘Home’ button to return to the home screen.

More information:

To add a shortcut for ‘Larger text’ settings to the ‘Control Centre’. See the article: Control Centre – iPhone/iPad/iPod Touch on this website.