Possibly you need to upgrade the IP phone firmware also. What are you using now ?
Download the TAR file with DST fix from CCO. Extract to router flash with
archive tar /xtract
configure each file for download with:
tftp-server flash:/ alias
If your router doesn't support directories (that is, less than 28xx) just use
tftp-server
and load under telephony-service, without the .loads extension
Hope this helps, if so please rate post!