If Auto-Lock is greyed out at 30 seconds and the battery icon is yellow, turn off Low Power Mode. Then open Settings → Display & Brightness → Auto-Lock and choose the delay you want.
01Turn off Low Power Mode
Section linkOpen Settings → Battery. On recent iPhones, look under Power Mode if Low Power Mode is not shown directly. Turn it off and reopen Auto-Lock. You can also ask Siri to turn off Low Power Mode. While Low Power Mode is on, it sets the delay to 30 seconds.
02Check what happens after you change the delay
Section linkLeave the iPhone unlocked on the Home Screen without touching it, and look away while you wait. Check when it actually locks. On supported models, Always-On display can still show a dim Lock Screen after the phone has locked. Keeping the unlocked display on for longer uses more battery.
03If you still cannot change the timer
Section linkConfirm the battery icon is no longer yellow and check the Auto-Lock page again. On a work or school iPhone, tell your IT team the Auto-Lock value you see and whether the control is greyed out. On a personal iPhone, share those details with Apple Support.