Welcome to the community, @Michael_Stout! :grinning_face_with_big_eyes: This should be possible. Are you saying that {gsm} is your field name containing the number? If so, this formula in a button field should do the trick:
IF(gsm, "https://api.whatsapp.com/send?phone=" & gsm)
That will create the link (activating the button) if there’s a phone number in the {gsm} field, and leave it blank otherwise.
However, be aware that it’s going to be a two-stage process. Airtable always opens URLs in the browser, and can’t be forced to target another application directly. When clicking the button, the URL would open in the browser first, which would then redirect to WhatsApp desktop.
