They are really important because they are so frequently used by Advanced or native speakers of English. It is natural for them to use them. Also, because they mean something completely different than the base verb used in the phrasal verb that it can be really hard to understand what it means. As a result you will have difficulty understanding some English speakers.
They also open up the door to your next level in language learning, where you go from a person who speaks English to a more advanced or native like speaker. This can be an important step for students who want to study abroad, people who want to travel and talk to other English speakers, or even for work or business.
We all dread the moment when we don’t understand something, but are sometimes too scared to ask for help. You don’t want to show that your English is not good enough. Therefore, focus on phrasal verbs and your confidence will grow along with your English vocabulary.