With minimal research online one can easily find that a prepositional phrase consists of a preposition and an object. Most online and paper resources will describe a preposition as a word that describes the relationship between two nouns/noun phrases.
For example
The cat is behind the table.
OR
The cat behind the table was eating the leftovers.
I know that you refer to behind as the preposition, the table as the object of the preposition, but am confused as to if there is a word to describe the relationship between behind and the cat. I am looking for a word for that specific relationship, not simply that in the first example, the cat is the subject of the sentence.