Unless you work for the phone company, your chances of finding what the “ANI” (automatic number identifier) number is month-by month are slim to nil. Around here, it changes frequently - apparently the phone company doesn’t want people to know what a given phone’s number is.
Fortunately, all you need to do is dial up your cell phone from that line, and the number should be displayed.
Of course, if you don’t have caller ID block on your phone (and I think there’s a * code that allows you to toggle on/off your caller ID info), you can call a cell phone, a friend with caller ID, etc, and get the number that way…