Hi Ron,
As per the the release notes for firmware version 9.3(1):
"The Cisco IP Phone 8941 and 8945 support a new "secure by default" feature with this release. Before phones are upgraded to Firmware Release 9.3(1), the Cisco Unified
Communications Manager must have devpack 8.0.3(24049)/8.5.1(14070)/8.6.2(22030) or higher installed. The phones require this devpack. If the correct devpack is not installed first,
the phones cannot successfully register to the Cisco Unified Communications Manager."
So, please install the required device pack on all the callmanager servers and restart the TFTP service on them and reset the phones. The issue will be fixed.
HTH
Manish