Really didn't expect responses ... those questions were 'food for thought' or investigation by op.
Hmmm .... '/home/phost/public_html/' is the sort of path/config one would find on a shared hosting box ... or one configured for shared hosting (allowing access to public_html of user accounts located in home. Guess I really didn't catch that. :\
If that assumption is correct, wonder if you have suPHP or some other add-on to PHP that providers use to protect customers from one another.
(include_path='.:/usr/lib/php:/usr/local/lib/php:/home/phost/php') ... hmmmm, your server is searching the above paths. Must be environmental paths of some sort.
php -i would/should have shown you a path or several paths depending upon what is installed.
On a Mac without Zend:
ENV["PATH"] => /usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin
On a CentOS 5. server, kinda depends upon how PHP was compiled ... ie, switches like '--with-png-dir=/usr' and config.
php -m might have shown:
[Zend Modules]
Zend OPcache
which means there is a opcache.ini in /etc/php.d/ ... this on a PHP 5.3.3 with Zend OPcache v7.0.3 that was installed manually.
Bottom line, CentOS server is flexible enough to be configured with 'not so common to typical' variables/locations, etc.. Difficult for programmers to take that into account. Hard to know exactly what the problem is ... not very good at Vulcan mind melds ... that's why the sig said ... in the spirit of thinkering.
Yours, in the spirit of sharing, Ken