I dont think you make much sense in what you have asked. You want to save flash movie files (FLV) from the likes of youtube. Get the unplug plugin for firefox. Just google for both as they are free. That then can be saved to a desktop. However you dont say what mobiles. My smart phone with a larger screen will play just about anything where as an older smaller phone wont play anything that is oversized for its screen.
Could you maybe explain further what you want to do.