It is repeating actually because you told it to do so here:
You would need no-repeat to stop it repeating:
However as there is no fixed positioning on an iphone so you will only get the image once and it will scroll away with the page. Maybe you could add a background-color for the iphone or merge/fade the image into the background-color at the bottom for a smoother effect.
There is no fixed value for background-position and you probably meant this:
background-position: 0 0;
You may be able to find a JS solution.