Marilyn, welcome to myphonetechs!

As you can see I moved your question to the Samsung forum.

the iDCS18d phone is compatible with several Samsung systems and programming does vary slightly from system to system. We will need to know which system you are connected to and you will need to have technician programming access to make the change. Do you have the technician level password to your system?
One other option for you to try is the in group/out group feature. If the phones were originally programmed to ring this option allows you to turn it on and off. You can try dial the following code from a non-ringing phone without lifting the handset; 53500. If you have this feature you will see in your display "group status" or get an error if you do not. Without knowing which system you have and how is was set-up, this is only a guess.