My father knows the owner of the store. What is the object of prepositional phase in this sentence

object = store

prepositional phrase = of the store

Explanation:

object: a noun or noun phrase governed by an active transitive verb or by a preposition.

prepositional phrase: a modifying phrase consisting of a preposition and its object.

In the sentence "of" is a preposition; the entire prepositional phrase is "of the store." The "store" is the object since it is governed by the preposition "of."