Here's why:
* Prepositional phrases start with a preposition (in this case, "on") and include an object (in this case, "his limousine").
* They function as adjectives or adverbs, modifying other words in the sentence.
For example, in the sentence "The man stepped on his limousine," the phrase "on his limousine" acts as an adverb, modifying the verb "stepped."