Suppose a live call gets interrupted and you want to call the customer back immediately. This is possible without leaving the current customer screen with the option 'Call another number' and then you just call Telephone1 again. see this instruction.
Another way is to pause after booking the call and then look up the last call (at the bottom) via the Orange 'Call log' button and click on Dial now, then in the Number options button call Telephone1.