I ran into this sentence while watching a TV show. Context: One person tried to call another person, but the latter didn't answer. So the first person came to the other and said as mentioned above.
In my understanding it is supposed to be a type of mixed conditional that refering to an unreal past condition (past perfect) and the probable result in the present (present conditional). With this said, the sentence should've been as follows: "If you had answered your phone, you would know.. ".