When I saw that Vim had these, I’ve upgraded and now use ctags and code completion from Vim.
To get code completion, I type out the little bit I know and then type ctrl-o and ctrl-x:
To get ctags working, I installed it using sudo apt-get install ctags and then at the root of all my php files I typed:
ctags -R .
This generated a tags file.
Now when I open any file and have the cursor over a function or class, I just type ctrl-] and the file containing the class or function opens up.