Final answer:
The prepositional phrase in the sentence is 'while in office' which provides additional information about when the presidents had beards.
Step-by-step explanation:
The prepositional phrase in the given sentence is: while in office.
A prepositional phrase is a group of words that begins with a preposition and usually ends with a noun or pronoun called the object of the preposition. In this case, the prepositional phrase 'while in office' modifies the verb 'sported' and provides additional information about when the five American presidents had beards.