Prepositional phrase follow by a noun.... preposition + noun
So in the sentence: A prepositional phrase will function as an adjective or adverb.
As an adjective, the prepositional phrase will answer the question Which one?
As an adverb, a prepositional phrase will answer questions such as How? When? or Where?
Boy with the Yellow hair = adjective because it answers WHICH boy? Boy with yellow hair.....
Ran home == adverb because.... it answers WHERE? We answer it.... he ran home...or ran home.
Hope that helped! :)