There are four main groups of phrasal verbs:
1. Transitive, separable
Transitive verbs have a direct object:
I switched on the light
Can you turn up the music please?
Put down your pens at the end of the exam.
The two parts of the phrasal verb can be separated by the object.
I switched the light on
Can you turn the music up please?
Put your pens down at the end of the exam.
If you use an object pronoun (me, you, him, her, it, us, them), it must go between the two parts of the phrasal verb:
I switched it on.
Can you turn it up please?
Put them down at the end of the exam.
2. Transitive, inseparable
These verbs also have a direct object but cannot be separated:
I'm looking for my pen.
He came across a new word in the article.
We've been working on the project for months.
Even if you use an object pronoun, you cannot separate these verbs:
I'm looking for it.
He came across it in the article.
We've been working on it for months.
3. Intransitive, inseparable
Intransitive verbs do not have a direct object. This type of phrasal verb can never be separated.
The plane took off.
His car broke down.
The dog ran away.
4. Phrasal verbs with three words
Some phrasal verbs are composed of three parts: the verb plus two particles. These phrasal verbs are transitive and inseparable.
He came up with a new idea.
I'm looking forward to meeting Sarah.
We need to get rid of the old washing machine.
Even if you use an object pronoun, you cannot separate these verbs.
He came up with it.
I'm looking forward to meeting her.
We need to get rid of it.
Remember that most phrasal verbs have several meanings, and the type can change according to the meaning. For example, to take off is intransitive and inseparable when it means that a plane leaves the ground, but transitive and separable when it means to remove clothes: She took her jacket off. See more uses of to take off here - you can also check the definition of any new words in the dictionary!