Accessibility Options For Failing Sight On Smartphones?

Quick back story: My mother has failing eyesight, well, failed in one eye, failing in another. I've managed for the last couple years to stay ahead of it by placing her on Windows Phone. The double wide large tiles, and blowing the font up all the way, make it incredibly easy for her to see on her Lumia 925. Lately though, I have noticed that it's harder for to see the large text. Window Phone 10 doesn't seem to have a triple wide tile enabled, so I'm seriously contemplating a move to a larger phone (iPhone 6+/Note) and iOS/Android.

(Use case for her is: Good camera, Facebook, Instagram, WhatsApp, Texting.)

Has anyone else encountered these problems? Any tips, thoughts or advice?