Why is my iPhone 6 silent mode turning on and off its self

Your Screen Shot tells me that your iPhone is connected to bluetooth headphones. When that happens that all notification sounds can be heard through the headphones.

Is it possible that you have these Bluetooth headphones that are in the ON position somewhere close to you and your iPhone automatically connects to it when both devices get closer? If this happens then you will hear no sounds on the iPhone and might think that Silent mode has been activated.

Axel F.

No idea what you think the screen shot you posted has to do with it… “Silent mode” is controlled by the physical ring/vibrate switch on the side of the phone above the volume buttons.