VPN Client use unique IP

Hello,

I have problem with my VPN, I don’t know to to fix it ?

My VPN server IP’s:
LAN: 192.168.10.1/24
WAN: 192.168.5.25/24
VPN POOL: 192.168.5.100-192.168.5.240

The Ip Address of client that use from Server is: 192.168.5.135
I’m using VOIP for communication from server to client but why in VOIP Server I can get only one IP from phones of VOIP 192.168.5.25 ?

Is there possible to get separated IP for each VOIP device or any other solutions that we can communicate with each other ?