Non-separable phrasal verbs i.e. you cannot separate the verb and its particle or, in other words, you cannot put the object between the verb and the particle

e.g. look for sth

I am looking for a job.

* I am looking a job for. = WRONG

Separable phrasal verbs

e.g. look sth up = find information in a dictionary, encyclopaedia or on the Internet

I will look up the meaning of this word.

I will look the meaning of this word up.

* I will look up it. = WRONG

I will look it up.

If you can separate a phrasal verb, you must separate it when the object is a pronoun.