When the phone is idle, it normally displays the date, time and extension number. It may also show a number if status letters at the bottom left.

B = Barred
A B is shown on your phone's display when the system administrator has set you to outgoing call barred status. You will only be able to make internal calls while this is applied.

D = Diverting (Forwarding) Calls
A D is shown on your phone's idle display when you have forward unconditional enabled.

G = Group Member (In Group)
A G is shown on your phone's idle display when have been configured as a member of a hunt group. While this is the case, you may receive calls targeted to the hunt group.

N = No Calls (Do Not Disturb)
An N is shown on your phone's idle display when you have do not disturb enabled. See Do Not Disturb.

T = Twinned
A T is shown on the phone's idle display if it is internally twinned with your phone. Calls to you will alert on both phones and can be answered by you at either phone.

S = System Alarm
If you are configured as a system administrator, an S in the phone's display indicates a system alarm.