Unfortunately, it seems that there is no way to permanently give a website access to the iPhone camera in Safari ( than ).
iOS 11 added the ability to completely disable camera and microphone access in Safari privacy and security settings. However, when the camera and microphone access are enabled for Safari, it only means Safari will ask the user for their permission when a site requests access to the user media.
Unfortunately, it is not possible to get additional network-specific settings from iOS 11.3,
so your users will need to confirm their permission each time the camera is needed on your site.
I would like to refer to the corresponding Apple Support page, but this question does not seem to be addressed there yet.