I’m not sure about editing on the phone but there is video editing software that you can use on your computer. Depending on what your are wanting to do will determine which software you will need. If you are looking for basic trimming, adding titles, adding music, transitions, Windows Movie Maker will work.
Windows:
– Windows Movie Maker (free, and usually already on most Windows machines)
– Sony Vegas (not free, but offers more functionality than WMM^ but might be harder to learn)
Apple:
– Final Cut (not sure if it comes preinstalled, if it’s free, etc.)
Also check out this list:
Wikipedia List of Video Editing Software