An issue was raised that this could result in nonsensical usage, e.g., type=email. This could be addressed with a schematron rule that requires used of PhoneContactMethod if type=phone and flagged as an error for any use of PhoneContactMethod combined with type=anything other than phone. This is what I recommend - we will need schematron rules for other items as well, which we are developing currently.
An issue was raised that this could result in nonsensical usage, e.g., type=email. This could be addressed with a schematron rule that requires used of PhoneContactMethod if type=phone and flagged as an error for any use of PhoneContactMethod combined with type=anything other than phone. This is what I recommend - we will need schematron rules for other items as well, which we are developing currently.