Phrasal verbs are formed from a verb and a preposition or an adverb. The reason why you need to learn them by heart is because you can’t simply guess what they mean from looking at them, even if you know the meaning of each part of a phrasal verb.
As your English is improving, you start to notice more and more the subtleties of the language. A good way to work on such details is by taking private English lessons so that a teacher can focus on your individual needs. You should also try to self-diagnose your problem areas.
One of the difficulties that students have when learning English is mastering the correct use of indefinite pronouns....