Not every verb followed by a preposition is a prepositional/phrasal verb. In many cases the verb is intransitive and is followed by a prepositional phrase. In those cases, the following noun would be the object of the preposition. When there is a real prepositional/phrasal verb, verb plus preposition is considered a unit, because of the idiomatic meaning. If this unit takes a noun, it is a transitive phrasal verb, and the noun is the direct object of the phrasal verb.
See more here: http://speakspeak.com/resources/engl...-phrasal-verbs
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