If you select Regular Expression, then it will treat it as a phrase. It is case sensitive, though. If you want to make it case insensitive, then select Regular Expression and enter:
[cC]reative [wW]riting [cC]hallenge
There are no quotes needed. Regular Expressions are a programming thing and they can be very powerful, but also very annoying. Wikipedia has a good summary:
http://en.wikipedia.org/wiki/Regular_expression#POSIX_basic_and_extended
If you use Regular Expressions for |OT| topics, then you'll have to account for the | being a character used in the Regular Expression language itself. Same goes for brackets, parentheses, periods, and the others on that Wiki page. You can get past this by using the \ character beforehand.
\|OT\|
Yes, that's a pain, but you can also use Regular Expressions to get rid of all |OT| topics including the numbered ones, like |OT2|, |OT3|, etc. by using the . (period) which stands for any character and the * (asterisk) which means zero or more of the previous character:
\|OT.*\|
That gets rid of all |OT| topics and the numbered ones, even something like |OT954|. And yes, you could do something like:
.reative .riting .hallenge
and that will take care of the case of the words as well, since the period stands for any single character.