How do we tell the difference between a prepositional phrase and a particle phrase?

From the Farlex Grammar Book, their main difference is that particles cannot introduce a prepositional phrase-a preposition + its object-while a preposition always does.

Please look over these proposals. Does these proposals function as the object of the preposition over, or is over merely a particle functioning adverbially with look?

He can’t get over her. Similarly, is her the prepositional object of over, or is over merely a particle?