Add value to session array

I try to create an array and add a value to it each time a new random number is generated.

When I generate a number, but the array stays at one value.

<?php
session_start();
$numbers = array();
$_SESSION["numbers"] = $numbers;

function getNumber() {

$getNumber = rand(1, 75);
return $getNumber;

}

?>

<?php 
if(isset($_POST['submit'])) {
    $numbers[] = getNumber();
    array_push($_SESSION["numbers"], $numbers);
    echo $numbers[0] . "<br>";
}
?>

How can I create a array which is filled each time a number is generated? Or do I need to create a db for this?