I tried a similar scenario: The phone has a nfc reader built in, so I put the tag on the charger and tried letting the phone read it, but quickly discovered that android can’t/wont read nfc tags unless the phone is unlocked, which defeated the elegance of the solution. I hadn’t considered buying a standalone reader and attaching the tag to the phones, that sounds a lot more complicated.
If answering the email requires writing a book to anticipate all the possible questions or options or complications that might come up, then no it’s not disrespectful to call someone instead.