I know it's a mouthful, but what it means is that there is a 指令所, a command base inside which different 指令員 (operators) work. Each operator is in charge of different matters (communications, equipment, etc.) and two of them are, therefore, the 運転指令員 and the 旅客指令員. The assumption is that each of them has a separate line (電話 in this case) to speak with the driver. Check the link for more information on what the 旅客指令員 does.