In order to enable pgsql support for PDO, PHP needs to be built with the configure option --with-pdo-pgsql[=DIR] where DIR is the path to the postgresql install directory or pg_config.
Alternatively, PECL can be used to install PDO drivers:
root@hostname# pecl install pdo_pgsql
However, from your reference to "easy apache", I suspect you're using cPanel and a hosting provider, in which case your question is probably better directed towards the support team of the company who you're paying.
Also, you should probably mention this and tag your question appropriately with 'cpanel' to make your question more likely to be found by people who have experience with your environment.