Hmm. The wording has me somewhat confused. Phrasal verbs is a term used to describe both verb-adverb phrases and verb + prepositional phrases.
Semantics aside, there are two simple tests that prove useful when determining the function of X in verb + X:
 a verb followed by a preposition forms an expression with an idiomatic meaning.
=> Is 'sailing through' an idiom?
 prepositions take nominal objects.
=> Is 'exams' the object of 'sailed' or the object of 'through':
Preposition + object: She sailed through them.
Verb + adverb: She sailed them through. (awkward)
We leafed through the book.
We leafed the book through. (awkward)
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