SIP INVITE Ghost/Bogus Calls - and Allow Direct IP Call settings

[complex1]

If you can’t or won’t change firmware or phone settings then it is hard to solve the issue.
If you have hundreds of phones I assuming you provisioning them. So changing port 5060 into 5070 can be done by changing the template and re-provisioning the phones. It is even possible to update the firmware by provisioning the phones.
But before doing this you can test this on a couple of phones before you re-provision all phones.
You have to do something...