Phrasal verbs consists of a basic verb + another word or words. The two or three words that make up a phrasal verb form a short 'phrase' - which is why we call them 'phrasal verbs'.
Phrasal Verb:
add (something) on(to) something and add (something) on
Meaning:
to extend something by providing more (of something). (This use of on with add is colloquial.)
Example:
You added nearly one thousand dollars onto the total.
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.