Polycom & 2 servers

I am using 2 Freepbx servers, 2 PRIs and Polycom 330 Phones.

I configured the Polycom phones through web interface not TFTP.

I configured 2 Servers on the Polycom phone on the same line (Line 1)

With the following configuration:

Server1 : Server 1 IP
Port: 5060
expire:3600
reigster:1

Server2 : Server 2 IP
Port: 5060
expire:3600
reigster:1

the phone is registered on the both of servers on the port 5060,
the incoming calls through the 2 servers are fine,
but when a phone makes an outbound call, it goes to the 1st server only,

when i make regsiteration on the 2nd freepbx server, with port 5061,5062,etc…, and on the phone in the section of the Server2, it’s not being registered.

Please how can i specify the phone to go to the 2nd server in case of the outbound calls.

Thanks