It depends on your callmanager group. if you did not configuration your CallManager Groups, and add the Subscriber into the group, then the phones will not fail over.
Do a quick test with a phone online, go into the settings and network configuration. Do you see you CCM 1 xxx.xxx.xxx and CM2 xxx.xxx.xxx? If you do not see CCM2, then you do not have your groups configuration correctly. The phones have no idea there is a second server in the cluster.
give that a whirl and see what happens.
Cheers