Emacs Lisp Package Archiver, simply a way to install emacs lisp script on emacs without wasting time on download, put where it could be loaded, load it …
It just install the package and let you use it. Command is M-x package-install RET [and choose the package].
It will install the package in the ~/.emacs.d/ELPA folder.
Some usefull php el editing packages:
https://github.com/arnested/php-extras some usefull extras, and completion integration
http://company-mode.github.io/ company mode: a drop down completition for function you are writing or via direct call
auto-complete auto completition (on C-M-i)
Speed up php writing with emacs!