In everyday speech, a phrase may be any group of words, often carrying a special idiomatic meaning; in this sense it is synonymous with expression. In linguistic analysis, a phrase is a group of words (or possibly a single word) that functions as a constituent in the syntax of a sentence, a single unit within a grammatical hierarchy. A phrase typically appears within a clause, but it is possible also for a phrase to be a clause or to contain a clause within it.
This is a companion discussion topic for the original entry at http://grammarerror.com/tags/phrase