HTML + JS validasi noHP.

<!DOCTYPE html>
<html>
<head>
    <title></title>
  <script type="text/javascript">
  function validasi_input(form){
  if (form.telp.value != ""){
  var x = (form.telp.value);
  var status = true;
  var list = new Array("0", "1", "2", "3", "4", "5", "6", "7", "8", "9");
  for (i=0; i<=x.length-1; i++)
  {
  if (x[i] in list) cek = true;
  else cek = false;
 status = status && cek;
  }
  if (status == false)
  {
  alert("Telp harus angka!");
  form.telp.focus();
  return false;
  }
  }
  return (true);
  }
  </script>
</head>
<body>

<form method="post" action="aksi.php" onsubmit="return validasi_input(this)">
<p>Telp/Hp : <input name="telp" type="text"></p>
<p><input name="" type="submit" value="Submit"></p>
</form>

</body>
</html>