Phrasal verbs, also called two-word verbs, are idiomatic expressions wherein the second element of the verb (the adverb or particle) is not necessarily predictable.
Phrasal Verb:
pile up
Meaning / Example:
1. [for things] to gather or accumulate. > The newspapers began to pile up after a few days.
2. [for a number of vehicles] to crash together. > Nearly twenty cars piled up on the bridge this morning.
A phrase that combines a verb with a preposition or adverb or both and that functions as a verb whose meaning is different from the combined meanings of the individual words