In general, you should be able to Turn OFF iPhone by using the power button. However, this method does not work on iPhone X, which cannot be shut-down using the Power button.
In-fact, the Power Button on iPhone X has been renamed by Apple as the ‘Side Button’ by Apple and it has been programmed to perform a variety other functions.
The power button cannot be used to Power-OFF iPhone X, because pressing the power button ends up activating Siri, which prevents you from powering off your device.
Hence, you need to get used to new way to switch-off iPhone X, which involves using both the Side and the Volume down buttons to power-off your device.
Steps to Switch-OFF iPhone X
With the Side button on iPhone X being programmed to perform other tasks like activating Siri, Accessing Apple Pay, activating SOS, you need to get used to the following method of switching-off iPhone X.
1. Press and Hold the Side and the Volume Up (or the Volume Down) button on your phone, until you see the ‘Slide to Power OFF’ option appearing on the screen of your device.
2. Simply, drag the Slider to the right and it will switch-off your device.
3. Patiently wait for your device to completely Power OFF.
When you want to switch-on iPhone X, press and hold the Side button again, until you see the Apple logo appearing on the screen of your iPhone.
Power Off iPhone X Without Using the Side Button
The following method can be used to switch-off any model of iPhone, including iPhone X and other models that cannot be powered-off using the Power button.
1. Open Settings > scroll down and tap on General.
2. On the next screen, scroll down to bottom and tap on the Shut Down option.
3. On the next screen, use the Slider to Power-OFF your device.
4. Wait for your device to completely Power OFF.
At any time, you can switch-on your device by simply pressing and holding the Side button.