Halliday & Matthiessen (2014: 413):
Phrasal verbs are lexical verbs which consist of more than just the verb word itself. They are of two kinds, plus a third which is a combination of the other two:(i) verb + adverb, e.g. look out ‘unearth, retrieve’
(ii) verb + preposition, e.g. look for ‘seek’
(iii) verb + adverb + preposition, e.g. look out for ‘watch for the presence of’