Yet phrasal verbs do permeate the language, particularly the more colloquial variety, the kind used for almost all spoken communication, so students do come across them all the time and usually take them in stride. This being the case, you can deal with them the same way you deal with other lexis: highlight them when they come up along with their collocations, then move on. Treat them as chunks of language.
For example, say in a lower level class you’re looking at phrasal verbs with “turn”, so perhaps a useful chunk of language would be “Shall I turn up / down the volume?”, “Shall I turn on / off the radio?” Actually at this point you may want to ask them what other words they think collocate with “turn on”. This is sometimes useful because students can try out their ideas, for example, you can “turn on the TV / the light / the heat / the air conditioning”, but you can’t “turn on your car”; you obviously “start up your car”.
When teaching phrasal verbs like this, there’s really no need to go into the minefield of whether this particular type has an object or not, or is separable or not. Just get them to learn (memorize) the chunk in question, for example, “Shall I turn off the radio?” This also completely avoids the issue of what happens when the object of the phrasal verb is a pronoun, that is, you can say “turn it off” but not “turn off it”.
This is what I mean when I say phrasal verbs are messy. You risk opening a Pandora’s box if you try to tackle this fiddly grammar too soon. But happily there’s no real need to: you can treat, “Shall I turn off the radio” as a chunk of language and leave well enough alone. Perhaps another day they’ll come across, “I’ll turn it off”, and then you can give a fast and friendly explanation of the variations, “I’ll turn the radio off” and “I’ll turn off the radio”, but for God’s sake, don’t get bogged down by this.
Again, it’s vital that they come away with practical, useful chunks of language like, “Shall I turn off the radio?”. Then later when you complicate the grammar they’ll already have been using phrasal verbs and hopefully be familiar with the examples you’re using. This will go far to bypass the confusion and demoralization that students so often feel when confronting this (for them) arcane grammar.
By the way, what we’re seeing here illustrates why lexis comes before grammar in the Lexical Approach. The lexis itself, the chunks of language, bring along its own grammar as we’ve been seeing, so if students learn “I’ll turn it down”, as part of the package they also get “will” for spontaneous decisions, and “turn it down”: the verb + object pronoun + particle.
If you approach this from the other direction and actually start out by writing on the board “verb + object pronoun + particle”, you’ll surely frighten your poor students off. And if they do stick it out, they’ll have learned some theory but not how to put it into practice. For that you’ll have to go back to useful chunks of language, which should have been your starting point anyway.
Meanwhile, long grammar explanations are normally a waste of valuable classroom time. So steer clear of the phrasal verb quicksand of over-analysis and instead give them useful chunks of language with minimal analysis. You won’t regret it.