There is a bug with latest firmware in that voice prompts for navigation from phone/earbuds cannot be disabled without also disabling navigation vibrate/beep alerts on the watch.
The position from Garmin seems to be that this is a feature, not a bug so might not be fixed. The only way it will be fixed is if enough people complain about it so if it's something that irritates you please add a comment to the following thread:
Thanks!