The closest PHP has to CPAN is PEAR (http://pear.php.net). It stalled for a long time, although development seems to have picked up a bit now that everything is on GitHub (https://github.com/pear/)
Composer (with http://packagist.org/) is getting popular in the PHP world.
I find it interesting that PHP doesn't have anything in the same league as Perl/Ruby/Python even after all these years.
Any PHP folk out there?