Help - new to php

<form action="test.php" method="POST">
<br>
<?php
    
    for ($i=1; $i<=6; $i++){
        echo $i.'<input type="text" name="option_"> '.'<br>';
        
  }
?>
 <br>

<input type="submit" name="submit" value="submit">

<br><input type="text" size ="2" name="add_field"> <input type="submit" name="add" value="add">
    Add extra boxes
    <?php
              $select = array();
                 if ($_POST['submit']){
                    for ($x = 1; $x<= 6; $x++){
                 if ($_POST["option_$x"]){
               array_push($select, $_POST["option_$x"]);
             }
        }
    if (count($select)){
    echo '<br>'.'<br>'.'<br>'."The Decider has choosen: " .'<p>'.$select[rand(0,count($select) - 1)].'</p>';
          }
    }
    ?>
</form>

Hi, I have 6 textfeilds and a submit button. When someone enters several values into the textfield and selects submit it will display a random result from one of the 6 textfields. I have also another textfeild and submit button. This is to add more textfields.
At the moment it is only displaying the result from the 6th textfield as I do not know how to correctly store the results into an array and also im unsure on how to add extra textfields. can anyone help please?