request suggestion for IP Sip phone using fix line

Hi Experts,

Recently we just setting up a new pbx voice cloud on our office, and we experienced some issue after that the phone becomes intermittently. In this scenario we have multiple WAN link in our peplink, and our service provider only allow one of the WAN 1 interface IP.

PBX voice cloud ip -
WAN 1 - WAN : Time

My question is how can we force the in-bound and out-bound traffic if the source or destination match our PBX public IP ( Between I have tried configure in the outbound policy force the traffic if match PBX public IP (, but the result still intermittently.

Please help & thanks in advance.