[Decode]

Можешь использовать атрибут pattern.

<form method="get" action="index.php">
  <input name="num" type="search" pattern="[\d()-]">
  <button type="submit" class="search-button">Искать</button>
</form>

<script>
  var inpElem = document.forms[0].elements[0];

  inpElem.oninput = function() {
    this.value = this.value.replace(/[^\d()-]/g, '');
  };
</script>