Helping out PHP development
As you should already know by now, PHP is an open-source development project - you can download the source, make changes, then send them back to the developers for everyone else to use. The development of PHP is done entirely by volunteers wanting to help out, and you can join them - even if you cannot program very well - or cannot program at all! - you can help out.
Here are things you can do to help:
If you cannot program, then submit bugs to the PHP bug database - if you find a problem, write in with a test case and how the developers can solve it. Be detailed - they need to know what operating system you have, which version of PHP, and more. Go to http://bugs.php.net to submit problems and view existing bugs.
If you can program, get in touch with the developers and ask how you can help. There are lots of outstanding features that need programming! Alternatively, look through the bug database, find an unresolved problem, and try to track it down - usually fixing bugs is the easiest way to start.
If you want to help other people learn PHP, subscribe to the PHP "General users list" from http://www.php.net/mailing-lists.php - people ask all sorts of questions there, and you can help answer them, or even ask your own.
If you just want to offer your opinions on various PHP-related matters, go to http://www.php.net/mailing-lists.php and subscribe to the "Internals list" - this is where the developers of PHP itself (not scripts written in PHP) talk about the language, bugs, new ideas, and new versions. Please respect the fact that the chances are you will be amongst the least-knowledgeable people reading the list - it is best not to charge in with rants about what is missing from PHP or even post to the list at all until you have been reading for a while and have an idea what is acceptable.
The only way PHP is going to grow and improve is by people helping out - even if you just fix one bug or answer one question on the mailing lists, it all helps. Go on - help out!