Call phone number with Microsoft Teams

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "div",
  "children": [
    {
      "elmType": "span",
      "style": {
        "display": "inline-block",
        "padding": "0 4px"
      },
      "attributes": {
        "iconName": "=if(@currentField != '','TeamsLogo', '')",
        "class": "ms-font-l"
      }
    },
    {
      "elmType": "a",
      "txtContent": "@currentField",
      "attributes": {
        "href": {
          "operator": "?",
          "operands": [
            {
              "operator": "!=",
              "operands": [
                "@currentField",
                ""
              ]
            },
            "='https://teams.microsoft.com/l/call/0/0?users=4:' + toString(@currentField)",
            ""
          ]
        },
        "target": "_blank",
        "class": "ms-fontColor-themePrimary ms-fontColor-themeDark--hover"
      }
    }
  ]
}