How do I turn off my iPhone 16 and turn it back on?

To turn it off, hold the power button and the volume up button until you see the slider to power off the phone. Another way is to go to settings, general, and scroll to the bottom and tap power off. To turn it on, press the power button until you see the apple logo.

FYI, iPhones do not provide a user-accessible “warm restart” function as do many other electronic devices. (including Macs)

The “Two Step” Off … On procedures — as kb1951 has posted — are the “normal” methods to perform the task.