Answer:
The person that is not necessarily on the phone now is Jane
Explanation:
Jane talks on the phone, this sentence is an example of the simple present tense, which is used to talk about routines and repeated and programmed activities which are not necessarily happening now but are constant.
Bob has been talking on the phone for an hour, this sentence is an example of present perfect continuous which is used to talk about an activity that started at some point in the past and continue in the present that means that Bob is on the phone right now.
Mary is talking on the phone, this is an example of present continuous, which is used to talk about the action at the moment, which means that it is describing what Mary is doing right now.