Private listening is a new feature that allows you to interact with Google Assistant and allows you to listen to audio files more privately without disturbing others.
When interacting with Google Assistant or playing voice messages via the Recorder, place the phone beside your ear and the audio will output through the handset without disturbing others around you. Move the handset away from your ear or press and hold the Volume Up button to have the audio playback through the speaker.
To turn this feature on, go to Settings > Advanced > Private listening.
Note: This knowledge is currently only applicable for ZenFone 6. Please stay tuned for further updates on ASUS Official Website.