As of this writing, Apple's iOS, which runs on its iPads, iPhones, and iPods has the most robust accessibility features for people who are blind or low vision. iOS includes a built-in screen reader called VoiceOver which reads screen contents aloud and allows a person to interact with the phone through gestures on the touch screen. VoiceOver works with all of the apps and functions that come with the device and also with a majority of the apps that can be downloaded from the Apple AppStore. iOS devices also offer a built-in screen magnification program called Zooms. There are also many ways to personalize the font size, color, brightness, and other features which can make the screen easier to see.
There are a variety of other cell phones that offer accessibility features. Learn more at the following links:
AT&T: http://www.wireless.att.com/learn/articles-resources/disability-resources/disability-resources.jsp 1-866-241-6568
Sprint: http://www.sprint.com/landings/accessibility/
Verizon Wireless: http://www.verizonwireless.com/aboutus/commitment/accessibility.html