phoneValidator.js

function validatePhoneInput(selector){
  $(document).delegate(selector, "keyup", function(e){

    function isNumber(n) {
      return !isNaN(parseFloat(n)) && isFinite(n);
    }

    function deleteLastChar(val){
      val = val.substring(0, val.length - 1);
      if(val[0] != '+'){
        val = '+7' + val;
      }
      $(this).val(val);
    }

    var val = $(this).val();
    if (val[0] != '+' && val.length == 1){
      $(this).val('+7');
    }

    if(!isNumber(val) || val.length > 12){
      deleteLastChar.call(this, val)
    }

  });
}
// validatePhoneInput('.typical-modal-new__mainform .number input, ul.callback li.tools input[type="text"]');