Several updates have been made to the documentation for the PHP-GTK project including a version of the manual.
From Leon Pegg on the PHP-GTK Community site:
I have been working on the php-gtk documentation the last few weeks. I finally have an updated version of the manual. Unfortunately its not on the main site gtk.php.net, so I have uploaded it here: leonpegg.com/php-gtk-doc
The manual includes tutorials, the actual reference guide and an appendix of details on terms/other information.