When the prepositional phrase does the work of an adjective, it is called an adjectival phrase.

It modifies a noun or a pronoun by answering the questions What kind? How many? Whose? or Which one?

Examples:

• The lady in the front row is smiling mysteriously.

• They moved the luggage of the guests to the room.

• The student lives in an apartment across the street.

In the above sentences, the phrase in the front row modifies the noun lady; of the guests tells about luggage; and across the street tells about the noun apartment. These are all adjectival phrases.