'Brightened up his day' is a nice expression, because it suggests that he was having a neutral kind of day - neither sad nor happy - and call brightened it up.

Cheer up is only really used when someone was sad etc before hand. But it can be used in a general way by some people, The call from his freind cheered him up. It may not have indicated he was unhappy in the previous sentences but the call did cheer him. But in majority of cases it is used to indicating someone cheering up after being sad/ill. You could say something like the following if they were not sad/ill before. He felt so happy after her unexpected call. Because she called, it gave him a big boost to his ego Her call brightened up his day. His day seemed brighter after her call. After her call, he had a smile on his face for the rest of the day.