Can’t call custom css in style.php

by

The easiest way to add dynamic CSS is to put it inside a callback and hook the callback into the template, e.g. via wp_head (or wp_print_styles).

You’ve not posted your code in full context, so you will need to modify to suit your specific needs. That said, here’s the basic principle:

Callback

function wpse_129259_enqueue_dynamic_css() {
    // Grab your variable
    global $data;
    ?>
<style type="text/css">
a {
    color:<?php echo $data['link_color'];?>;
}
</style>
    <?php
}

Hook

add_action( 'wp_head', 'wpse_129259_enqueue_dynamic_css' );

Using style.php

You can put your dynamic CSS in its own PHP file, then simply include it inside your callback. e.g.:

function wpse_129259_enqueue_dynamic_css() {
    // Include dynamic CSS file
    include( get_template_directory() . '/style.php' );
}
add_action( 'wp_head', 'wpse_129259_enqueue_dynamic_css' );