The .phar lib is used for creating PHP archives. PHP 5.3 always has this extension built-in, but hosting teams may disable it for some reason.
To enable it, try the following:
Contact your hosting team and ask them to do it for you.
Your server’s control panel may have tools to enable PHP extensions. Check your hosting Knowledge Base for more info.
If you are the hosting owner, you can download the .phar lib here http://pecl.php.net/package/phar and install it according to the instructions given.