Why doesn't # and * work in Phone actions?

Apple doesn't support those characters in the URL scheme for the phone app. Here is their official stance:

“To prevent users from maliciously redirecting phone calls or changing the behavior of a phone or account, the Phone application supports most, but not all, of the special characters in the tel scheme. Specifically, if a URL contains the * or # characters, the Phone application does not attempt to dial the corresponding phone number.”

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