Try this, found on another forum with same issue.
Go to settings.
Apps and notifications
App permissions
Phone
You'll see a list of all applications only focus on the ones that are toggled active.
Start at the top and disable the first one.
Toggle Bluetooth off and on and test to see if you get phantom call.
If you do get the phantom call re-enable calling access for that app and repeat these steps down the list.
Some services will warn you that it will break functionality. This is fine as you will most likely be re-enabling.
Once you locate the offending app remove it, leave the calling functionality disabled, and/or inform the developers of the issue. For me I still need the app but will leave calling disabled unless I need it.
