This is a good question. I looked up some phrasal verbs to see if there were any I didn't know (there had to be!) an lo and behold, I found some.
A few examples: argue down, argue out, bail up, beaver away, and big up.
Without the context these were nearly impossible to guess. However something I do is take the meaning of the individual words and pair them together to create meaning. I would guess 'argue down' means to beat someone at an argument because you're a) arguing and b) going down on them, and that implies giving them a good thrashing, so I'd assume that you're winning. Turns out I'm right. 'Beaver away' is easy to guess because you just have to think what a beaver does traditionally - work hard. And that's exactly what the phrase means. Not all phrasal verbs are like this though, especially ones that have their origins outside America (at least from my experience).