I suspect this is likely a phone firmware issue. To upgrade the phone firmware you will have to upgrade the NetVanta 7100 firmware too. In the release notes for each version of NetVanta 7000 firmware there is a section that details the minimum phone firmware required depending on the phone model. Given some of these are on 4.12.00.E, I would first make sure you have the proper boot code on your Netvanta 7100s so you can upgrade them to a current version of AOS. This post explains how to check the version information: Upgrading Netvanta 7100 from to A4.03.00.SC.E
If you don't have the proper boot code you will need to open a ticket with ADTRAN support to get it. Once you have the proper boot code running, I would start by upgrading the 7100 to R10.9.3, which is our current extended maintenance release. Then you can also upgrade the ADTRAN IP 700 phones to 2.4.1. Make sure you save a current copy of your configuration for every unit before upgrading and put them in a safe place. Several commands have changed in this jump of firmware and it is always a best practice to keep an archived copy of your configuration for a particular version in case you need to revert.