The PR with the update is here: https://github.com/docker-library/php/pull/1694

Looks like we need to be patient:

> Why is this not merged yet?

> I'm not a maintainer and can not merge this. Please wait until a maintainer has come around to look into this.

> This is merged, but I cannot find the image?

> After this PR has been merged, more steps are to be taken, including an upstream merge on docker-library/official-images and subsequent image builds. For a full description of the timeline, please refer to docker-library/faq#an-images-source-changed-in-git-now-what.