On an iPhone or iPad you have not supervised, a profile can genuinely block: it filters every app, works on mobile data, and applies to pages opened inside other apps. What it cannot do is stop you from removing it, or from switching DNS back to Automatic. Those settings exist but Apple restricts them to supervised devices, which means erasing the phone first. See Lock the DNS profile.
So this is worth doing, and it is not a lock. Pair it with a Screen Time passcode someone else holds, which is protected as long as the Apple Account entered at the passcode-recovery prompt is the trusted person's or the prompt is skipped, and with a record someone else can see, so that removing this is visible rather than silent.
Watch this: Apple's developer documentation marks the DNS Settings profile payload as deprecated from iOS 27 and macOS 27. It still works and still installs today, but Apple has put it on notice, and the replacement is delivered by device management rather than by a profile you tap. Re-test this profile after updating to iOS 27, and expect the route to narrow over time.
Build your profile
What this does not cover
- Other devices. A profile applies to the device you install it on. Do this on each one.
- Apps that are not browsing. Content inside a feed you have allowed is untouched. See Shrink the window.
- Your own determination. You can remove this. On iPhone that is the honest limit, and it is why a trusted person matters more than any setting on this page.
- Windows, Android and Linux. They have no equivalent to Apple profiles. Set up filtered DNS covers those.