1. A computer-implemented method comprising: obtaining, from a phrase-based index for an Internet search engine, a list of documents from a collection of documents available via the Internet that contain a first phrase, the first phrase being relevant to a query; for each document in the list: determining, using related phrase information stored in the index for each document in the list of documents, whether the document includes one or more related phrases of the first phrase, where each related phrase has an actual co-occurrence rate of the related phrase and the first phrase in the document collection that exceeds an expected co-occurrence rate of the related phrase and the first phrase in the document collection; ranking the documents in the list based on a quantity of related phrases determined for each document, so that documents with more related phrases are ranked higher than documents with fewer related phrases; and selecting at least some of the highest-ranked documents to include in a result to the query.