Currently when you attempt to navigate to a blocked site, the redscreen page is served from https://metamask.github.io/phishing-warning/v3.0.0/.........
The warning page is our authority page to let users know of a scam they are about to visit. If we continue to serve it on non-metamask.io domain, we are training users to trust non-metamask domains for this security control.
Moving to metamask domain will isolate it from the rest of the metamask experiments that are served under metamask.github.io/<your page>
Ref Links

Currently when you attempt to navigate to a blocked site, the redscreen page is served from
https://metamask.github.io/phishing-warning/v3.0.0/.........The warning page is our authority page to let users know of a scam they are about to visit. If we continue to serve it on non-metamask.io domain, we are training users to trust non-metamask domains for this security control.
Moving to metamask domain will isolate it from the rest of the metamask experiments that are served under
metamask.github.io/<your page>Ref Links
https://github.com/search?q=org%3AMetaMask+metamask.github.io%2Fphishing-warning&type=code
extension https://github.com/MetaMask/metamask-extension/blob/develop/development/build/scripts.js#L191
also some ledger thing also served from here: https://github.com/MetaMask/metamask-extension/blob/develop/offscreen/ledger-iframe.html
mobile doesn't seem to be serving the same page lol. It's serving a page that apparently ships with the app?
https://github.com/MetaMask/metamask-mobile/blob/main/app/components/UI/PhishingModal/index.js