An app can legally link into its own section of the Settings app, and if it uses CallKit, it can link into the Call Blocking & Identification section. Linking anywhere else into Settings is making use of private URL schemes and is supposed to not be permitted and the app rejected during submission.
However the Robokiller app deep links into the Settings app with the page scrolled down to where the Phone section is. How are they doing that? Is there some new API that permits the app to link to there? Or are they making illegal use of private URIs and have been getting away with getting past App Store review for years?