Answer : by my aunt
The complete prepositional phrase in the sentence above is "by my aunt". A prepositional phrase usually is made up of a preposition at the start and a noun or pronoun at end that serves as the object of the preposition. It may also serve as an adjective or an adverb in a sentence. In the statement "The red coat was sent by my aunt", the preposition is by followed by the object of the preposition my aunt.