how do i set up a phantom extension such that one of my co lines rings to it (and doesn't ring any other phones?). currently i have an icd group with no members which i'm using for this but i wonder if it creates other issues.

Take a slt port that does not need to receive calls
or is not used at all, set up call fwd all in Maint Console to Vmail pilot ext.
DIL the line iquestion to that slt port say 105 (at nite), set up a mailbox for 105, ext =105, all calls xfer to mailbox = no. Set up a message wait button for mailbox 105 on whatever phones its needed on.