#div_id_phone_number fieldset {
    display: block; /* default block layout so legend stays full width */
  }

  #div_id_phone_number select,
  #div_id_phone_number input[type="tel"] {
    display: inline-block;
    vertical-align: middle;
  }

  #div_id_phone_number select {
    width: 90px;
    margin-right: 8px;
  }

  #div_id_phone_number input[type="tel"] {
    width: calc(100% - 100px); /* Adjust based on select width + margin */
  }