They only appear when you are actively on a phone call, and they are non-removeable. If this is the case and they are actually missing, I'd suspect that something you have installed recently is creating a problem.
Reboot and see if the problem persists.
If yes, then go into Settings > Manage apps, and disable any recently installed apps.
If the problem is gone, re-enable apps one-by-one and place a test call after each one to determine which one is the cause.
If the problem persists, then clear cache and data on the Phone app. This will also erase all call logs.