Minifie style.php in head of index.php

i currently have an wordpress theme options page. I read all the theme options styles in style.php which i then include in the head of my website.

Does anyone know how to minify this style.php file?

most of the "on-the-fly" scripts offer an solution, but it changes the header which results in an error message "headers already sent".

header.php:

<style>
    <?php require_once('css/style.php');?>
</style>

style.php:

<?php
?>
body {
    background-color:<?php global $variable; echo $variable['color-background'];?>;
    font-family:<?php global $variable; echo $variable['typography6']['font-family'];?>;
}

a {
    color: <?php global $variable; echo $variable['link-color']['regular'];?>;
}

<?php

?>

does anyone have a solution?