Of course you can do policy route on ZS.
Go to Network -> NetBalancer -> Balancing Rules and Add a new rule according to the criteria you have. Then you specify from which WAN link it will be routed. In case one WAN link fails, everything will be routed to the other.
As I said before for your example just tag the telephony and data traffic to prefer the links you want. The rest of the traffic will be automatically load balanced between the links. In case one link fails all traffic will be forwarded via the link that is still up.