When you read something on your iPhone, you can use the zoom in and zoom out feature without using the font setting for increasing the text size. If you feel comfortable with smaller text size, then maximum content gets added in your smaller screen. There are two options to change the font size on your iPhone, first is in Settings and second in Control Center. So here are some steps to follow for changing text size.
Please read the originial post here: http://msofficeoffice.com/blog/how-to-change-the-text-font-on-your-iphone/