Algorithm for grouping sentences by phrases

Hi, We have a long list (100000) of short sentences and the need to group them together. Each sentence should be assigned to a group which consists of an 'important' phrase. A phrase of length N means N words from a sentence in any order. Each group is named after the phrase. The 'importance' of a phrase is the number of occurrences of that phrase in all in sentences. Because the order is not important, phrases such as "how are you" and "how you are" are equal. Look at [login to view URL] to see an example and some other requirements. Thanks very much!