I have a ge27851f-2 cordless

If the base station is plugged into the phone line you should be able to designate one phone as the master. That phone should be on the base station when charging. If you look in the manual it should show you how to redo the master. It's usually just pushing a button when on the station. Just takes a second. That will also enable the phone to work with the base station. It locks out any phones that haven't been physically connected to the bases. To do the second phone you may have to do a slightly differant process to register it with the bases.