Inseparable Phrasal verbs

Some phrasal verbs cannot be separated. 

Who looks after the baby when you're at work?

Even when there is a pronoun, the verb and particle remain together.

Who looks after her when you're at work?

With separable phrasal verbs, the verb and particle can be apart or together.

They've called the meeting off.

OR

They've called off the meeting.

However, separable phrasal verbs must be separated when you use a pronoun. 

The meeting? They've called it off.

Phrasal verbs are very common in English, especially in more informal contexts. They are made up of a verb and a particle or, sometimes, two particles. The particle often changes the meaning of the verb.

I called Jen to see how she was. (call = to telephone)

They've called off the meeting. (call off = to cancel)

In terms of word order, there are two main types of phrasal verb: separable and inseparable.