Check your CallManager groups. If the Publisher is not in the group for the phones to failover, then this is your problem. If you go to an IP Phone and hit the settings button, look at the CallManager information. If you only see the subscriber, then the phones have no idea there is another server they can failover to.
If you just added the Publisher to the CUCM group,then you will need to restart the device pool and reboot all the phones. This will then allow the phones to download the new configuration changes.
cheers!