fix on/upon

phrasal verb

fixed on/upon; fixing on/upon; fixes on/upon

1

: to direct one's attention or thoughts toward (something) : to focus on (something)

He has fixed on/upon the idea of going back to school.

All eyes fixed on her as she entered the room.

2

: to make a decision about or choose (something)

After weeks of discussion, they've finally fixed on a solution.