A group of words may take the place of a part of speech.
PHRASES : A group of connected words, not containing a subject and a predicate, is called a phrase. A phrase is often equivalent to a part of speech. Adjective or adverbial phrases consisting of a preposition and its object, with or without other words, may be called prepositional phrases.
CLAUSES : A clause is a group of words that forms part of a sentence and that contains a subject and a predicate. A clause used as a part of speech is called a subordinate clause. Clauses of the same order or rank are said to be coördinate.