Hi, there could be several reasons for this but I'll also give you some background on it too.
Check DLIS for the port. You could have a 120D plugged in where at 280D used to be and it's mismatched. If so, you'll see the P_TYPE and I_TYPE are different and just Update it to the correct type. This is probably what has happened.
Or you have it plugged into an SLT port instead of a digital port. But you'd probably get Phase 0 in this case.
Or you have a FlexSet plugged into an old type digital card only meant for the DKT series phones.
Check those 3 things and it should sort it out. Below is some background on the Stand Alone Modes. What version/type of system do you have? Which country, US?
there are 3 Stand Alone Modes:
1) Phase 0 Completed - Hardware initialization completed; did not execute step 2
2) Phase 1 Completed - Layer 1 initialized; did not execute step 3
3) Phase 2 Completed - Layer 2 initialized; did not execute step 4
When the phone starts up it goes through the following sequence:
Step 1: Initialization of Hardware and Memory
Step 2: Initialization of Layer 1 communication - component synchronization, communication with Coral card
Step 3: Initialiization of Layer 2 communication - Line Access Procedure (LAP-D) with respect to card
Step 4: Initialization of Layer 3 communication - the main program initializaes and associates the relevant database areas for the keyset
When the telephone initialization program is running, an asterisk (‘*’) is displayed on the phone’s LCD display and the 4 steps listed above are carried out. In the event that
the initialization is not completed (Layer 3 was not reached or did not initialize within 10 - 20 seconds) the telephone will go into Stand-Alone mode.