Phrasal Verb Vs Prepositional Phrase [Diagnostics]

Halliday & Matthiessen (2014: 326-7):

… in some instances, such as act as, turn into, the preposition as, into was so closely bonded with the verb that it should be analysed as part of the Process. … The boundary is indeterminate; but [the phrasal verb] analysis is suggested where the verb could not easily occur without the prepositional phrase, or is separated from the preposition thematically.