I created 2 text fields. One called Telephone and one called Telephone URL. I kept the Telephone URL a text field and not a URL field. I enter the telephone number in the first field and then the second I entered tel:01234567890. I use Elementor page editor so it was easy enough to select the ACF Telephone Field for a telephone number and the ACF Telephone URL field for the link. Elementor used the text and made a link of it. No coding required. Maybe if you have a page editor program you could use this method too.
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