Where in the Call Manager do I configure SRST so it lets the phones know what router using SRST.
SRST is configured on your IOS gateway, not in call manager. Your IP phone has to have a phone load that supports SRST as well. If you are running CM 3.1(3a) or higher, you should be ok.
In the gateway, the command is
ip source-address port 2000 strict-match
I stand corrected, it looks like in CCM 3.3, you can define a device other then your LAN GW as a SRST device!