Final answer:
An adverbial phrase is a prepositional phrase that acts as an adverb, modifying a verb, an adjective, or an adverb in a sentence to provide information about time, place, reason, or manner.
Step-by-step explanation:
An adverbial phrase is a prepositional phrase that acts as an adverb. It modifies a verb, an adjective, or an adverb in a sentence to provide information about time, place, reason, or manner. For example, in the sentence Pierre quickly ran through the main points of his argument, the adverbial phrase quickly describes how Pierre ran.