What is the prepositional phrase in following sentence Alan dropped paper under desk. desk below?

The prepositional phrase in the sentence "Alan dropped the paper under the desk" is "under the desk".

Here's why:

* Preposition: "under" is the preposition.

* Object of the preposition: "the desk" is the noun that follows the preposition and receives its action.

The prepositional phrase acts as an adverb, telling us where Alan dropped the paper.