Phrasal verbs often include adverbial prepositions like out, in, through, over, back, etc. These function like the prefixes in Russian verbs: вы, в,про, пере, etc. Sometimes they change the meaning of the main verb, other times they give it a perfective aspect. I would recommend a good dictionary where you can study the general meanings of these adverbials.
вы = out
высказаться = speak out, express/state one`s opinion
up = Russian perfective aspect
eat = Did you eat soup? = вы ели суп?
eat up = to eat all of (something) Did you eat up the soup? = вы сели суп?
The phrasal verbs that don't include prepositions must be memorized--there is no other way to learn them. It takes a long time to master a language, perhaps a lifetime of study. Good luck!