Phrasal verbs are very, very flexible expressions, so a single definition is usually misleading or wrong. For the second part of a phrasal verb (eg. "up"), it's a very bad idea to look for one single definition - you'll end up making even more mistakes in English! However, sometimes "up" (as well as "down", "out" and "off") can suggest the action leads to a certain result. This is hardly a perfect explanation and you will find hundreds if not thousands of exceptions, but it may sometimes clarify a subtle difference.