An adverbial phrase is a group of words that functions as an adverb in a sentence. It provides additional information about a verb, adjective, or another adverb, often indicating how, when, where, or why something happens. For example, in the sentence "She sings with great passion," the phrase "with great passion" describes how she sings. These phrases can be made up of various parts of speech, including nouns, adjectives, and prepositions. They enhance the meaning of a sentence by adding context. For instance, in "He arrived after the meeting," the phrase "after the meeting" tells us when he arrived.