A prepositional phrase is a phrase that begins with a preposition and ends with that preposition's object. Prepositional phrases can be either adjectival or adverbial. The red phrases below are examples of prepositional phrases in English.
Answers the question "where?" and is therefore adverbial.
Answers the question "when?" and is therefore adverbial.
Answers the question "which love?" and is therefore adjectival.
Answers the question "how?" and is therefore adverbial.
See here.
See here.