Awareness of structures may be conscious or unconscious in the expert user of a language: this paper contends that insufficient conscious awareness of a language structure in teachers of English may impair the teaching and learning of that structure, even when considerable classroom time is invested in it. Phrasal verbs are extensively covered in modern ELT textbooks yet they remain notoriously difficult for learners of English to acquire. This, I argue, is at least in part because teachers are insufficiently aware of the systems that underlie them. This paper looks at different levels of language awareness in relation to phrasal verbs and suggests that a heightened conscious awareness of their underlying semantic systems may improve the language teacher's effectiveness in teaching them. A semantic analysis of phrasal verbs is proposed for the language teacher, based on the notions of transitivity and compositionality. It suggests that teachers of English need to be able to identify and classify any phrasal verbs they encounter and that the notions of transitivity and compositionality should enable them to classify phrasal verbs into three basic types: directional, idiomatic and aspectual.