How to set up an ip phone so that it works through Pfsence?

Question

Telephony

Please help me in which direction to dig.
set up Pfsense in this way, set up an L2TP tunnel on the router. Connects to PF. I connected a Panasonic IP phone to the router. I turned on DHCP on the phone (distributes a router) received the address 192.168.3.0 (this address was set in PF)
The PBX has an Ip address of 10.0.2.15/255.0.0.0/10.0.2.2.
The telephone set is connected and registered to the PBX 192.168.3.0/255.255.255.0/192.168.0.15 (router address)
After connecting the tunnel, the PBX pings. The phone rings, but the interlocutor is not heard in the receiver, but he hears me.

Answer 1

if you look through the tracert command 10.0.2.15
192.168.0.15
192.168.3.0
10.0.2.15

Answer 2

On the pfsence machine, do a tcpdump and SDP analyze who and what ports are participating in your conversation.
You can put the dump on the file exchange, we can see.