The simple answer was already given:
No, you can't monitor that system if encryption is enabled unless you happen to have one of the radios that's used for that system and it has the necessary settings enabled to provide for decryption as required. While it might be technically possible in some manner to create some haphazard workaround with various types of SDR software and hardware, the encryption itself will stop you cold every time and unless you have access to the necessary system and radio-specific info (as mentioned above) you're just SOL, period, end of story, that's the ballgame folks.
I mean really.
As for using smartphones, well, smartphones using cellular technology is a completely different thing from traditional point to point radio communications, with vastly more coverage capability simply because of how cellular technology works (albeit some radio systems can patch through and allow someone to make or receive an actual "phone call" and that's been a capability for decades now). And go figure: cellular technology uses encrypted communications by default.
Also, smartphones allow for more precise forms of communication overall and not the half-duplex style (one person talks at a time, etc) that traditional radio communications are designed to function with. And sometimes it's just easier to use a smartphone so you're not tying up the actual radio comms with chatter that doesn't necessarily need to go out for every individual on the system to hear.
If you happen to have a Janek's Box type thing, by all means, listen in on anything your ears want but until you do, encryption is quite literally a wall of soundproof material between you and what those ears might wish to hear.
Seeing as the OP has made 2 posts and is obviously new to these surroundings, this should be a good lesson from the gitgo: encrypted comms are essentially not able to be monitored without access to the actual authorized radio hardware in use on the system itself - even if you had the necessary third-party capability to monitor an encrypted system, doing so would be against the law in most every country in the world so here's another lesson of sorts: the encryption debate with respect to radio comms is a very hot and delicate subject here at RR even in casual discussions, so be aware of that.
