All hail PhoneGabe!
<img src="http://oi44.tinypic.com/2z3utlz.jpg" border="0" />
(sorry, i could not resist the urge
to post this little funny image)
But if we are being serious, you might want to post more details of this issue - did you change any settings when exporting for PhoneGap? Did you change the image compression setting, by any chance? Are you sure that the .zip file was created and uploaded properly?
What do you mean, exactly, by saying that it didn't work? Was it replaced by a solid color, or did you get some other type of problem? A crash, perhaps? Are you sure that it's exactly the image that's to blame? Are there any specific blend modes set/any webgl effects that are applied to it?
Furthermore, what kind of image is it? A png-8 or png-32? Perhaps you edited it and accidentally exported it to png-24? I think that we really could use a bit more detail here, to be able to help you better... Could you perhaps take a picture of what exactly's happening?