How to Assign a Single Phone to Multiple Extension - Using Shared Call Appearance

Each phone are usually assigned to 1 primary user then can be assigned to other users using Shared call appearance, Busy line indicator, etc. 

When assigning a phone to multiples users, you will need to use shared call appearance feature. Therefore, to view, add or modify a phone shared call appearance, you will need to do the following:

a- login to 
b- change view from basic to advance 
c- on left side click admin settings 
d- click on button assignment 
e- in the drop down of select devices, locate the MAC address of the phone you which to assign to different extension/users
f- now you will see option from Button 1 to button 6 (depending on phone models, some could be 4, 6, 8, 12) for your phones (button 1 & 2 are the personal extension of the user)
g- now you can modify the buttons (example 3 to 6) and use them as Shared call appearance (you need to do them in order ex:3,4,5,6) 
f- if you need to modify button 3 but button 4 has something assigned to it, button 4 needs to be removed before button 3 can be edited 

Once you have edited the phone, wait 3-5min then reboot the phone. Once rebooted the phone should show the button assignment you have completed on the portal.