I am making iPhone build from mac mini,
at here, texture import settings allow RGBA32 bit.
but is this maintained when launched on real iPhone? or automatically changed to PVRTC washed, poor texture?
Yes happens all my projects also, yellow warning message.
Therefore manually need check and make changes.
See http://docs.unity3d.com/Documentation/Components/class-Texture2D.html and search for iOS. All your texture format problems are now solved.