We do not have an ERD posted anywhere of the database. (Don't know why, as it would have helped when I was just starting to code!).
You could probably try:
PHP Code:
if (is_member_of($touser,6))
Not sure if that would work, but if you have a test site then you can test it out.
edit: You said you modified the phrase and added that in? Hmmm, I would not have thought that php would work in it. :/