If you keep using them, you will not forget them. But it's difficult to keep using them if you are not in an English-speaking country! The best thing to do is keep on watching British/Canadian/Australian/American films/TV, and read lots of books/newspapers in English, and sing along with songs in English, and those phrasal verbs will become natural. In time. I'm afraid it takes a long time. So be patient. Don't worry. There are lots of websites where you can practice English phrasal verbs/idioms etc. Just keep clicking on them and doing a few exercises.