The 280 can have 2 digit extensions. I believe you need to make the Phdn ring in *81,*84,*87 for the CO. Then in that Phdn make the vmid code 14 and call forward all calls to another phdn. Put the second phdn on the phones as well as the first phdn on one phone. Then in 81,84,87 make those phones ring on the CO. Also need to make sure *80 is enabled. #603 on the second phdn to VM and call should follow id code of the first phdn. Something like that.
I am pretty sure that I have been to locations installed by other techs that use a DN, and not a PHDN, in program *81 and the system seems to want to follow the call forwarding and VMID of the extension in PRG *81.
Also, I would assume that you want to remove the voicemail ports from program 82 or 83 so the voicemail system does not answer before the call forwarding kicks in.