All phones that display Caller ID simply show the data received after the first ring. That is, the Caller ID information passes to the phone between the first and second ring. The only exception is if you programmed a different name for the number in your phone’s directory.
With that said, there are several thoughts that might explain what’s happening.
Either the data is being truncated due to some problem prior to reaching your phone, or your service provider is just sending one digit (although I never heard of that happening).
Another reason for this... If you have your phone behind your own PBX (a personal phone system), then that might be responsible for sending just one digit to your phone.
If you suspect your phone carrier, call them and explain the problem. If you have a PBX, contact the installer to find out if they can make a programming change to fix the problem.
One more reason I can think of... If you programmed your name directory and for some reason you placed single digits 1 through 9 in the name field for each contact, the phone would be replacing the incoming Caller ID with that.
The phone does indeed replace the Caller ID with the name you entered for the number. That’s is a feature of the phone. So if you used digits instead of names, that would definitely explain your problem.