Using $_POST then $_FILES to upload a file in PHP

I'm trying to write an upload form that creates a new folder in S3 based off of the name given in the isset($_POST[]). The problem I'm having is that it seems I can either use $_POST or $_FILES, not both, at least sequentially.

I tried nesting the if(isset())s, but that seems to not affect anything and from what I'm reading, nesting like this is frowned upon.

Here is a rundown of the code in question:

First, while selecting a lesson to view, a POST is done so I can get a name for the new folder to store this lesson (so they aren't all dumped in a bucket).

//view description and files for that lesson
    if(isset($_POST['viewlesson']))
    {
        $select = "SELECT * FROM lessons WHERE idlessons='$_POST[hidden]'";
        $selq = mysqli_query($con, $select);
        ?>  
        <table align="center" cellpadding="0" cellspace="0" border="0">
        <tr>
        <td><strong>ID</strong></td>
        <td><strong>Name</strong></td>
        <td><strong>Subject</strong></td>
        <td><strong>Grade</strong></td>
        <td><strong>Tag</strong></td>
        </tr>
        <?php 
        while($row = mysqli_fetch_array($selq, MYSQLI_ASSOC)) 
        { 
            echo "<form action=index.php method=post>";
            echo "<tr>";
            echo '<td>'.'<input type=text name=id   readonly            value="'.$row['idlessons'].'"></td>';
            echo '<td>'.'<input type=text name=name readonly            value="'.$row['Name'].'"></td>';
            echo '<td>'.'<input type=text name=grade readonly           value="'.$row['Grade'].'"></td>';
            echo '<td>'.'<input type=text name=subject readonly         value="'.$row['Subject'].'"></td>';
            echo '<td>'.'<input type=text name=tag readonly             value="'.$row['Tag'].'"></td>';
            echo "</tr>";
        } 
        ?>
        </table>

        <?php 
        //debug to display post before upload
        $tokey = $_POST['name'];
        echo $tokey;

Here is the form that loads once a lesson is selected to "View". If I take it out of this isset and upload to it before the view, the file will upload fine, but I have to specify my own folder. As such, I left it inside as I don't want the user to be able to upload to nothing.

        //upload form
        ?>
        <center>
            <form enctype="multipart/form-data" action="viewdb.php" method="POST">
                <input name="file" type="file">
                <input type="submit" value="Upload">
            </form>
        </center>
        <?php
    }

Lastly, we have the putObject method to s3. This is what happens when a file is selected and "Upload" is pressed. The way I wanted this to work was by using the $tokey as the new folder name, but since the isset isn't firing in the first place, I can't do that.

    //upload file to the bucket
    if(isset($_FILES['file']))
    {
        $file = $_FILES['file'];        
        $name = $file['name'];
        $tmp_name = $file['tmp_name'];      
        $extension = explode('.', $name);
        //$extenstion = strtolower(end($extenstion));       
        $key = md5(uniqid());
        $tmp_file_name = "{$key}.{extenstion}";
        $tmp_file_path = "files/{$tmp_file_name}";      
        move_uploaded_file($tmp_name, $tmp_file_path);          
        try 
        {
            $s3->putObject([
            'Bucket' => $config['s3']['bucket'],
            //'Key' => "uploads/{$name}",
            'Key' => "{$tokey}/{$name}",
            'Body' => fopen($tmp_file_path, 'rb'),
            'ACL' => 'public-read'
            ]);
            unlink($tmp_file_path);
        } 
        catch (S3Exception $e)
        {
            die("There was an error uploading your file.");
        }   
    }

I tried using unset($_POST); at the end of each if statement still to no avail. Is there a better way to structure this so both if(isset()) statements can run successfully, or am I kidding myself that this can be done? Any enlightenment on this is greatly appreciated!

Best,

-bromeo