sit up

Definition: to make someone suddenly pay attention to something.
(This verb has more than one meaning)

E.g.1. The talk was quite boring until he started talking about his personal life, and then everyone sat up and started listening.
E.g.2. In an interview, you want the panel to sit up and notice you, not forget your name as soon as you’ve left the room.

This phrasal verb can’t be separated.