关于选择下拉传递php变量的建议

I have the follow situation and what I like to do:

1. The user need to change an amount in a dropdown (select)
2. Depend what he choosed, he will get different select/option in the next dropdown

So far so good, it does in a not nice way (in my eyes) what I need. Anyone has a better solution how I can realize it?

    <div class="form-row field_select">
<label>Please select the amount of PAX/Passengers:</label><br>
<div class="select-box">
<span>Select the amount</span>
<form action="" id="myform" method="POST">
<select class="" name="amount_pax" id="amount_pax" onchange='this.form.submit()'>
<option value="NO" selected>Select the amount of passengers</option>
<option value="4">1 - 4 Passengers (PAX)</option>
<option value="8">5 - 8 Passengers (PAX)</option>
<option value="12">8 and more Passengers (PAX)</option>
</select>
</form>
<?php $samount_pax=$_POST['amount_pax'];?>
</div>
</div>
<div class="form-row field_select">
<label>Please select the amount of PAX/Passengers:</label><br>
<div>
<select data-placeholder="Choose Your Accommodation..." class="chosen-select" tabindex="2" name="price" id="price">
<option value="no accommodation was selected"><?php display_text("res_1_9") ?></option>
<?php
switch ($samount_pax) {
case "4":
$mysqli->set_charset("utf8");
$query = "SELECT Hotellist.hotelname, Hotellist.location, Hotellist.price44 FROM Hotellist ORDER BY Hotellist.location ASC";
$result = $mysqli->query($query) or die($mysqli->error.__LINE__);
while ($row = mysqli_fetch_array( $result, MYSQL_ASSOC)) {
echo '<option value="'.$row['price44'].'">'.$row['hotelname'].' ('.$row['location'].')</option>'."
";}
break;
case "8":
$mysqli->set_charset("utf8");
$query = "SELECT Hotellist.hotelname, Hotellist.location, Hotellist.pricebus FROM Hotellist ORDER BY Hotellist.location ASC";
$result = $mysqli->query($query) or die($mysqli->error.__LINE__);
while ($row = mysqli_fetch_array( $result, MYSQL_ASSOC)) {
echo '<option value="'.$row['pricebus'].'">'.$row['hotelname'].' ('.$row['location'].')</option>'."
";}
break;
case "12":
echo "12";
break;
default:
echo "Your favorite color is neither red, blue, nor green!";
}
?>
</select>                                      
</div>