You can install pdo_pgsql via two methods
1. Via pecl
pecl install pdo_pgsql
If this fails, enable it via manual compilation below
2. Manual compilation
Download the PDO driver from the PECL website below.
http://pecl.php.net/package/PDO_PGSQL
Download it and enter the downloaded directory by
wget http://pecl.php.net/get/PDO_PGSQL-1.0.2.tgz tar -xzf PDO_PGSQL-1.0.2.tgz cd PDO-PSQL-1.0.2/
Once this is done, run the standard commands for building a PHP extension.
phpize ./configure make make install
Once this is done, you can add the extension to php.ini.
cd /usr/local/lib/ vim php.ini extension=pdo_pgsql.so
Finally, restart Apache
service httpd restart
Verify it via commandline
php -i | grep pdo_pgsql