The symbol indicates the kit is in discreet mode, the call is being handled by the phone. This can be activated manually by pressing the GREEN button whilst already on a call or this can be a compatibility problem between the two devices.

If nothing has changed recently, I would recommend resetting your phone. To reset, turn the phone off and remove the battery leaving this off at least one minute before replacing and switching the phone back on.  When you next enter the vehicle see if this has resolved your observations.

Kind Regards