Does Phonak Virto 312 have a flight mode?

Yes, Phonak Virto 312 has a flight mode.

To activate it open the battery door of the hearing aid, then hold down the push button for seven seconds while closing the battery door. While in flight mode, the hearing aid will function normally, but will not be able to connect to or stream from a paired Bluetooth device. To exit flight mode, simply open and close the battery door.