i see no problem in your code however note that not all phrasegroups are loaded on all vbulletin pages ... and that might be the cause of your problem at the top of vbulletin source files you will find
PHP Code:
$phrasegroups = array();
there you find what phrasegroups are loaded by which pages ...for example if your phrase should show up in the members profile of a user at your board (member.php?u=$userid) then your phrase must be in a phrasesgroup that get's loaded when that page is viewed or you won't get any output