How am I able to allow the second query in this snippet to pass the value from the first selection onchange to the next? whenever I put the variable in the query, it does not recognize the change, but if I manually code the where clause, it works:

<?php

$conn = new mysqli("localhost", "root", "", "kevvskustomsdb");

$sql = mysqli_query($conn, "SELECT Device FROM devicetype");

?>
<form action="">

            <label id="level3-label" for="device-repair-type">Device to be Repaired</label><br>
            <select id="device-repair-type" name="selectform">

                <?php

                while ($row = $sql->fetch_assoc()){
                    $device = $row['Device'];
                    echo "<option value='$device'>$device</option>";


                }

                ?>


            </select><br>
            <label>Device Model</label><br>
            <select id="device-model" name="selectform">
                <?php
                echo "hello";
           $receiveDrop = $_POST[$device];
                if(isset( $receiveDrop ))
                {

                $sql1 = mysqli_query($conn, "SELECT Device FROM phonedata WHERE typeOfdevice = '$device'");
                while ($row1 = $sql1->fetch_assoc()){
                    $device1 = $row1['Device'];
                    echo "<option value='$device1'>$device1</option>";
                }
            }
                ?>
            </select><br>
            <label>Repair Type</label><br>
            <select id="repair-type-2" name="selectform">
                <option value="Select">Test</option>
                <option value="Custom Computer">Test</option>
                <option value="Repair">Test</option>
                <option value="Repair">Test</option>
            </select><br>
            <div class="button-css">
                <input id="submitbutton-repair-form" type="submit" value="Submit">
            </div>
        </form>

I tried passing and using _post, but could not get it to function. I will also be using the same solution for the third drop-down as well.

Thank you!