Terry,
Do not modify the "voice-port" for the CO-Line. This will not effect the label shown on the phone.
You will need to find the "ephone-dn" for the CO-Line. Will look something like this:
ephone-dn 588
number 3A10 no-reg primary
lable CO Line 1
trunk A0 monitor-port 0/1/0
If you want to change the label on the phone, modify the "label" for that "ephone-dn"..
Thank you,
Darren