Creating 'clickable' Phone numbers in Lists

I have created an MS list that contains a phone # column that I would like to be a 'clickable' link that would prompt to dial the number.  

I have edited the column in SPO and added the following JSON code.  This makes the links live in SPO, and the desktop version of Lists, but does not work on iPhone.  It opens up in an editor when i click on the number.  

Is this a bug in the lists app, or does anyone know the fix for this?   I have also tried replacing TEL: with callto:  with no luck. 

{
"$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
"elmType": "a",
"txtContent": "@currentField",
"attributes": {
"target": "_blank",
"href": "='tel:' + @currentField"
}
}