Since VoIP devices use various RTP ports, it is recommended to set the QoS rule by IP.
Assume the VoIP device behind Vigor3300 is with IP 192.168.33.100.
Please follow the steps below to configure QoS rule.
Set the real bandwidth of WAN1.
Note: if the set bandwidth is much lower than the real bandwidth, it will affect the performance.
Go to QoS>Outgoing Class Setup page to set the class name and reserved bandwidth.
Note: the reserved bandwidth percentages will be the total upstream bandwidths
Go to QoS>Outgoing Class Filter to add a new rule.
Input IP 192.168.33.100 with subnet mask 255.255.255.255/32 then select the class.
The QoS rule for reserving 20% bandwidth for IP 192.168.33.100 is done.
Then you can try and see if VoIP calls are made smoothly.