index.html
----------
<form action="deneme.php" method="post">
    <input type="text" name="cal" />
    <button type="submit">Cal</button>
</form>

deneme.php
------------
<?php

$cal = $_POST["cal"];
function calculation($cal){
    $matrix1 = array();

    for ($row = 0; $row <$cal; $row++) {
        for ($col = 0; $col <$cal; $col++) {

            $matrix1[$row][$col] = rand(10, 99);
        }
    }
    return $matrix1;
}
$matrix1 = calculation($cal);

echo "<pre>";
var_dump($matrix1);