Just quick thought try lldp see if its the same least youll know then if its specific to cdp feature , you may have hit bug
just wondering as well if the phones were already on the network they should have had a ip address what happened for them to go try get another one , did they reboot, switch flip etc ? phones will only request an ip during boot usually which makes me think something may have happened on switch if it happened to all phones or else the phones lost connectivity to the CM