“ So what have you been getting up to while I’ve been away ? ”
- to 'get up to something' means to do something - it's familiar and friendly.
It's usually used as a question to someone you know well.
There is another colloquial phrasal verb expression 'get down to' , which means to work on something -
'When are you going to get down to doing that job ?'
'When is he going to get down to work ?'
'They arrived there and got straight down to work.'
'Let's get (straight) down to business.'
To get straight down to something means to do it immediately /right away.