In iOS 7 and later, you can change the size of your font in Mail, Contacts, Calendar, Phone, Notes, and other apps that support Dynamic Type.
Change the font size
In iOS 8, go to Settings > Display and Brightness > Text...
Launch the Settings app from the Home screen of your iPhone or iPad.
Now tap on General.
Scroll down and towards the bottom, tap on Accessibility.
Tap on the Speak Selection option and turn it...