Not sure what are you trying to achieve, why do you want to turn off DHCP during the upgrade?
Do you want to avoid the phone to upgrade the firmware, you can use phone load option on the device page if thats the case.
Anyways, two options one is statically key in the network information on the phone or you can use DHCP static/manual bindings;
http://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfdhcp.html#wp1001108
-Terry
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