KISS Grammar Workbooks
What Is a Prepositional Phrase?

     Prepositional phrases are simply prepositions plus the noun or pronoun that answers the question “What?” after them:
 
“to the house”
“under the desk”
“from the street”

Thus, to identify prepositional phrases you need to recognize prepositions and then make a question with “What?” after them – “Under what?” – “Under the desk.”

If a verb answers the question “To what,”
it is probably not a prepositional phrase.