I had the same problem. I disconnected the battery (by pulling out the little connector with the three coloured wires), reconnected it and the phonebook reappeared!
Could be line cord connection at base or other wiring issue. Do you have a different phone(s) at same location that work?
If you have a known good phone, the simpler the better, unplug all other tele devices at your location and verify the know good phone works?