How can I achieve this with dual wan?

I have a client that has 2 slow DSL connections. We want the general internet to go out DSL1 and VOIP traffic only to go out WAN2.

With v18, how is the best way to set this up from beginning to end? I tried using SD-WAN policy routing but for some reason that made the phones eventually have SIP registration errors.

Here is what I did below:

DHCP -> 

Reserved IP's for all VOIP Phones to a specific set

Firewall rules ->

Created a LAN, Phones to WAN, 3cx Any Service  Accept rule

NAT rule ->

Used the "default snat IPv4" rule

SD WAN IPv4 Policy Route ->

Source Phones Dest 3cx Any, Primary Gateway WAN2

Source LAN (minus IP's phones have), Dest any, Primary Gateway WAN1

This apparently doesn't work. I must be missing something simple.

Thanks.