I think iPhone’s auto focus is excellent. Especially iPhone6, 6Plus.
Generally, we don’t need manual focus.
If you use manual focus, touch “AF” button to change FocusMode.
Then, Focus Slider & Focus Value are appeared.
Focus Value is in the range of 0.0 – 1.0.
Note: Please look at photo of the moon. I have checked infinity, Focus Value is 0.7 (or 0.6?).
So, Please check your own iPhone. 1.0 is over infinity maybe.