Phrasal verbs are either separable or nonseparable. Unfortunately, there is no rule that will help you to look at a phrasal verb and always know whether it is separable or nonseparable.

Separable phrasal verbs

Separable phrasal verbs can be separated by their object. When the object is a noun, it is usually entirely optional whether the object is placed between the verb and the particle or placed after the particle. Both sentences below are correct:

I took my shoes off.

I took off my shoes.