The verb phrase of the second sentence, however, has the idiomatic meaning of "to complete with ease and speed." It can only have this meaning if s...

The verb phrase of the second sentence, however, has the idiomatic meaning of "to complete with ease and speed." It can only have this meaning if sail and through are paired together. Changing the preposition would also completely change the meaning of the verb phrase; therefore, it is functioning as a phrasal verb.