Sounds like the DHCP Server issued the IP of one Phone to another phone when it realized the first phone was not available. Therefore when the phone with the actual IP Address came up and requested the same IP Address, there was a conflict in the DB. Clearing ip dhcp conflict cleared the IP Address DB and re-issued another IP to the Phones. I've seen this one in the past and clearing ip dhcp conflict does solve the issue. Though I'm not sure as to why this happens. You might want to post the same question on the LAN discussion forums. Someone who is more familiar with IOS based DHCP would be able to answer this question better. AFAIK, this is a DHCP issue and not a Phone issue