You can also do this easily on a per-directory basis using the Apache (assuming this is your web server) configuration file (e.g. httpd.conf)
<Directory /var/www/vhosts/domain.tld/httpdocs>
php_admin_value open_basedir "/var/www/vhosts/domain.tld/httpdocs:/var/www/vhosts/domain.tld/zend"
</Directory>
you can also completely remove the restriction with
<Directory /var/www/vhosts/domain.tld/httpdocs>
php_admin_value open_basedir none
</Directory>