In order to enable Dynamic Type in your iPhone running on iOS 7 beta 2, just go to Settings—>General, scroll down you will see Siri Spotlight Search, and then Text Size. Tap there.
Right now you will see a slider just like the one in the picture above… Using this slider you will be able to increase/decrease the size of your preferred text. Any apps that support Dynamic Type will “adjust to your preferred reading size below,†says the screen.
Now,when you’re using apps like Mail, iBooks, or others that support Dynamic type, the font will be large enough (or small enough) to fit your own personal preferences. Neat! Enjoy all and don’t forget to share this tip with your friends…