By unlocked, do you mean your iPhone doesn't go dark after a period of time? Did you check Settings > Display & Brightness > Auto Lock - change how long the screen remains open there. Also, if your tag line is correct and you own iPhone 15 Pro Max, you can manually lock the screen anytime by simply tapping the side power button once. If you use Face ID, you won't have to enter your passcode when you unlock the screen. But you always HAVE to enter your passcode to update the phone, after you update the phone the first time to get back in and after you power off the phone and turn it back on. To power off an iPhone 15 Pro Max, press and hold either one of the volume buttons and the side power button at the same time, then swipe to power off when it appears.