Getting custom phrase

[squishi]

The following is about the subscriptions.php in the Admin panel.

I have created the custom phrase "setting_zombaio_siteid_title" with content "Site ID".

An excerpt of the script:

PHP Code:

$phrasegroups = array('subscription', 'cpuser', 'stats');
//...
//test echo
var_dump( $vbphrase["setting_zombaio_siteid_title"] ); 


The phrase is echoed as being null.
Do I have to load a certain phrase group to get this phrase?
How would I add the custom phrase that I created to the 'subscription' phrase group?