Hi Italki friend " A phrasal verb in present day English is a verb that takes a complementary particle which is an adverb resembling a preposition, necessary to complete sentence. (E.g. He fixed up the car.).
The expression phrasal verb refers, in English Grammar, to a combination of a verb and a prepositional or adverbial particle, in which the combination often takes on a meaning which is apparently not the simple sum of its parts, for example turn up meaning appear. Longman Dictionary of phrasal verbs defines phrasals as "idiomatic combination of a verb and adverb, or a verb and preposition (or verb with both adverb and preposition)".
Phrasal verbs are considered to be a very important and frequently occurring feature of the English language."
Source: A HOLISTIC APPROACH TO PHRASAL VERBS. Andreea-Rosalia Olteanu. Editura Sfântul Ierarh Nicolae.2012.
I hope this fragment can help you :)
phrasal verbs are generally a combination of a verb + preposition. For example: break down, calm down, catch up, etc.see the below video.
I think it is combination between verb and particle, such as go away, pick up, take off, etc. And I think these words must be memorized and you must understand about the meaning and the way of using