It's a good idea from time to time to update your copy of the phpdoc tree so that you always have the latest copy. Currently, changes to the tree are made daily so you should always update your copy before making changes yourself.
To update your copy, cd to the phpdoc directory and issue the following command:
$ svn update
If you have also checked out any translation modules, those will also be updated with the command shown above, so there is no need to separately update your checked out translation modules.
If you only wish to update a particular file or set of files you would like to modify, you can pass their filenames along with the update command:
$ svn update file1 file2
If the files are located beneath the top level phpdoc directory, use the relative paths of the filenames:
$ svn update en/language/file1 en/chapters/file2