I agree completely with Joe. You can also have: - I'm not up to it or up to the job (I'm not good enough or I'm not ready) - He's up for elimination (in a reality tv show, when someone is going to be voted off) There are so many uses for these phrasal verbs, my recommendation is when you read a book or watch a ted talk and highlight every time it's used, write it in your notebook and think about what it might mean in that context. Or book yourself in for a general lesson with a great teacher and you'll cover phrasal verbs as part of the syllabus. I hope this info helps! - Katherine

Both are very casual expressions. "Up to" refers to something that a person is doing, whereas "up for" refers to something a person wants or would be willing to do. "What are you up to?" = casual / (normally friendly) way to say, "What are you doing?" "They're up to no good." = "They're doing something bad / against the law." "Are you up for ice cream?" = "Do you want to eat ice cream?" "He's up for anything." = "He's willing / open to do anything."