Not to step on your toes glasner, as it is an easy mistake to make, but match type DOES NOT affect quality score. All keywords on phrase and broad match are judged ONLY on instances in which the search query precisely matches the keyword, regardless of match type. This is referred to as the exact match subset.

You can find more info here: http://www.rimmkaufman.com/rkgblog/2010/09/28/negative-keywo...

Do you maintain "scent" from keyword to ad copy for this keyword? http://www.grokdotcom.com/topics/senseofscent.htm

If scent is not maintained you are hurting your clickthrough rate which accounts for a majority of the weighting behind quality score.