This is a very common question that causes lots and lots of confusion.
The choice comes down to the format of the control channel, not whether the voice signals being transmitted are analog or IMBE encoded.
If the radio system is a Motorola system using a 3600 or 4800bps control channel, it's "standard". If the radio system has a 9600bps control channel that conforms to the APCO-25 Common Air Interface (CAI) standard, it's P-25.
Systems that use either of these control channel types can have BOTH analog and digital IMBE encoded (A.K.A. P-25) audio.