An adjective prepositional phrase is a phrase contaning a preposition plus a noun (or a group of them) The prepositional phrase (P.P) is considered to be functionally adjective when it gives more information of a noun which could be subject or direct object.

In the example below, we say the sentence in bold is an adjective prepositional phrase because it names only one girl among other possibilities. The girl doesn't dance well because of the dress, so we couldn't say the P.P has incidence in the performance of the verb.

The girl in the red dress dances well.



If the red dress had certain power in it that makes the girl dance well even though she doesn't, it'd be functioning as an adverb and it should be arranged in the sentence like this.

The girl dances very well in the red dress.

Of course, it doesn't make any sense to write something like this unless you're telling a story in which clothes have power over people!