Well I'm guessing that you want to remove everything before the phrase then something like this will do:
s/.*?yourPhrase/yourPhrase/
The .* means match any character zero or more times.
the ? means that the previous expression should be non-greedy which means that if you have the same phrase twice in the string it should match on the first.
So the meaning of this substitution regexp is to substitute anything preceding and _including_ yourPhrase with the string yourPhrase and thereby removing the "anything preceding".