What if Apple 6splus receives information without sound?

The reason for this should be that the phone is set to silent mode or do not disturb mode, so just turn it off.

To turn off the mute mode, just turn on the mute button at the top left of the phone.

To turn off the Do Not Disturb mode, just turn on the phone and slide it up from the bottom, and then click the little moon icon to turn it off.