By the end of June 2022, the Debian Stretch LTS has reached the end-of-life for LTS and it has been switched to Extended LTS mode.

The PHP packages for Debian Stretch as available from DEB.SURY.ORG are no longer built and published. All packages have been completely removed on 2. July 2022.

If you absolutely need PHP packages past for the Debian Stretch ELTS and upgrade to Debian buster or (even better) Debian bullseye is not an option for you, the availability of the packages from the PHP LTS by Freexian will be unaffected and you can get PHP packages for Debian ELTS as a paid option.