thanks for the help Lingdian. I allready did that. But i found out that not types of media will work on the phone. If i use the same type as my phones creates (.mp4). then it works in the editor, but also on the phone 
But still the problem stays unfortunalely. If i put the mediatexturematerial on a plane, it works, but when i try to use the media in a widget, i doesnt work. And again, it works in the editor, but stays black on the phone!
the attachment shows this widget, the texture is the running mediafile (short mp4 movie)