I have the same question. For me at least, the issue it is trying to solve doesn't exist. I can't see it existing for many other people either, at least not to the extent that they need something like this.
The advantage with the standard is that my phone proposes from itself what it would do when I click a "tel:" URL or "mailto:" URL. And what I do most is just long-press and copy to clipoard. As this uses the native UI from my mobile OS, this just feels better then a HTML-rendered custom UI.
This is one of the old and golden web rules: Don't surpise the user with some UI he would not expect. Be consistent to the standards.
One thing I would like on Desktop (maybe it exists and I'm missing it) is to have Chrome's context menu show "Copy Phone Number" like it shows "Copy Email Address" because copying the link includes the tel prefix and it's annoying to remove for some workflows.
