I was just about to leave the office when the phone started ringing (point) `->` I was ___________________________ when the phone started ringin

=> I was on the point of leaving the office when the phone started ringing.

be on the point of ~ be about to: sắp xảy ra trong tương lai gần, sắp sửa làm gì

started Ving: bắt đầu làm gì