Been using this video editing app for about a year now. I use it about once a week. It's quite powerful and will do UHD video processing. It has the normal transitions and effects of your average editor on the computer. Also there is the ability to download from an ever growing list of title graphics, frames and so on. If your phone has good graphics processing than it will not take that long to turn out a final product. I am using it on my LG G4 and it does just fine. It normally takes 12 minutes for an 8 minute video to process in Full HD for me. There is also a top of the line photo editor by the same company you can use on the phone with stickers, frames and effects. Links Below.
Price of the full version of both at this moment is $7.99