have (one's) undivided attention
To be the sole thing that one is focused on. OK, now that your sister's asleep, you have my undivided attention—tell me what happened earlier. You will have their undivided attention if you have your lawyer send them a letter.
get/have somebody’s undivided atˈtention
(often humorous) receive somebody’s full attention: I’ll just finish writing this sentence, and then you can have my undivided attention.