Phrasal verbs are verbs which are always followed by an adverb, e.g. cloud over, a preposition, e.g. come across sth / sb, or an adverb and a preposition, e.g. creep up on sth / sb. The meaning of a phrasal verb is sometimes obvious from the meanings of its parts, e.g. fall down. But the meaning is often more idiomatic and so less obvious, e.g. put up with sb / sth. Phrasal verbs can be either transitive or intransitive:

When you get to the next crossroads, turn off.
Would you turn off the radio, please.

• A preposition can sometimes follow a verb which is not a phrasal verb. The preposition is part of a prepositional phrase:

Who lives across the road?

• Some prepositions commonly follow certain verbs because of meanings and collocation:

This broken plate will have to be paid for.
What are you looking at?

• When a phrasal verb is transitive, we can place a noun object before or after the adverb:

Please turn the radio off. Please turn off the radio.

• When the object is a pronoun, it is always placed before the adverb:

Please turn it off.

• With a verb + preposition, the preposition is placed before its object. We can't put the object between a verb and a preposition:

I've come into money.
I came into it when my father died.

• Verbs + adverb + preposition behave in the same way as verbs + preposition:

You'll have to put up with them for a little longer.

Note that many prepositions can follow passive verbs. However, the most common are by (used to mention the agent), with (used to mention how something is done or what it is done with) and in:

They're being cared for by a neighbour.
It was prepared with great patience.
Man was first discovered in East Africa.

• We use other prepositions when the meaning or verb + preposition collocation requires them:

Money has been contributed towards the costs.