It seems that feature is only available on certain phones. From contributor Servant of Cats:
The feature might only be present on a few iPhones – ones with a multi-LED array for Adaptive True Tone flash.
AppleInsider – How to adjust the flashlight's focus and beam shape in iOS 18
Reddit – iOS 18 Flashlight supports beam width
According to the comparison tool on Apple's site, the following phones have Adaptive True Tone flash:
- iPhone 14 Pro and Pro Max
- iPhone 15 Pro and Pro Max
- iPhone 16 Pro and Pro Max
The regular iPhone 14, 15, and 16 models do not have Adaptive True Tone flash –and without a multiple-LED flash array or adjustable optics, there would be no way for them to control the beam width.
The iPhone 14 Pro and Pro Max might not have gotten the beam width feature even though they apparently have hardware that might be capable of supporting it.