To switch off iPhone, there is a trick. Not as easy as an Android device. There are two methods to switch off your iPhone device.
The last method works for all iPhone models. Check All the Details.
Press and hold the power button along with the volume up or down button > Slider Apear > Move the slide to switch off.
Press and hold the power button or Sleep/Wake button > Drag the slider to switch off.
Go to settings > General > Shut down > Move the slider to switch off.