First, a phrase is any multiword group without a conjugated verb. Second, an adjectival phrase is a phrase that modifies or describes a noun or pronoun. Usually, an adjectival phrase consists of an adjective and a prepositional phrase, such as free from bias or pertinent to our discussion.
Other phrases, like prepositional phrases (over the rainbow) or verbal phrases (sitting next to the judge) may act as adjectives. We prefer to limit the expression adjectival phrase to those multiword groupings that begin with true adjectives.