My iphone turns on while on sleep mode?

So you press the lock button, the screen blanks, and eventually the phone battery is then eventually depleted? That’s normal.

The screen being blanked is a power-saving measure. The iPhone does not shut down when you press the lock button.

During normal use, iPhone is powered up and operating, even with the display blank. Some battery power will be consumed, as the iPhone is booted and running. The iPhone is able to receive notifications, play music, receive email, and receive text messages and telephone calls in this state.

If you want to shut down the iPhone, then follow the restart sequence as far as dragging the slider to power off the iPhone. No calls will be accepted, no messages will be received, and negligible battery power will be consumed.

If your iPhone display screen is lighting up and going dark of its own accord and repeatedly, then there’s likely some sort of a hardware problem here, and your iPhone will probably need service. Contact Apple Support, or your preferred service provider.

Unless you shut off your iPhone, it’s active—what’s commonly called “sleep mode” controls how quickly the iPhone screen dims and blanks, or how quickly the iPhone requires a passcode or Touch ID or Face ID input. But i]unless the iPhone has been shut down, it’s still active.