User guide for iphone Numbers

There is no User Guide for the iPhone Numbers app per se, however, there are planty of useful sources of information available:

The Numbers Help - found under the Wrench Menu in the upper right hand part of the application

Getting Started - a biref tour of the Numbers features - located as a document withing Numbers.app

Video Tutorials for using Numbers for OSX - http://www.apple.com/iwork/tutorials/#numbers - these provide basic functions and concepts but there are differences between the iOS version and the OSX version of Numbers, still usefull, though.

iWork '09 Numbers and iWork '09 Formulas & Functions User Guide - http://support.apple.com/en_US/manuals/#iwork

Both of these guides are in downloadable PDF Format and well worth having on your iOS device as general references since most features work in both OSX Numbers '90 and iOS Numbers 5 - you can also get the Pages and Keynote User Guides from the same location - keep them all handy in your iBooks Library.

There are also many videos on YouTube that you may find usefull.

Good Luck

There is a "Getting Started" document included with the iOS version of Numbers. You can read it on your iOS device or save it to your computer via iCloud or iTunes.