Go to Network > VLAN > LAN Networks:
Enter desired LAN name (Can be anything) and click Add New
Enter a new IP address for that LAN (For example : 192.168.2.1) and save settings
Go to VLAN Networks
Select Port Based VLAN mode
Click Add
On newly added VLAN select newly created LAN network
Switch port that are you going to use for VOIP device to ON (Example LAN port 3 to ON)
Now, VOIP and other LAN device traffic should be separated.