<?php
$sql1 = "SELECT * FROM likes WHERE id_user='$_SESSION[id_user]' AND id_post='$row[id_post]'";
$result1 = $conn->query($sql1);
if($result1->num_rows > 0) {
?>
    <a class="post-add-icon inline-items" disabled>
        <svg class="olymp-heart-icon">
            <use xlink:href="svg-icons/sprites/icons.svg#olymp-heart-icon"></use>
        </svg>
        <?php
} else {
?>
            <a href="#" class="post-add-icon inline-items" id="addLike" data-id="<?php echo $row['id_post']; ?>" onClick="return false">
                <svg class="olymp-heart-icon">
                    <use xlink:href="svg-icons/sprites/icons.svg#olymp-heart-icon" id="addLike" data-id="<?php echo $row['id_post']; ?>"></use>
                </svg>
                <?php
}
?>
                    <?php $sql2 = "SELECT * FROM likes WHERE id_post='$row[id_post]'";
$result2 = $conn->query($sql2);
$totalLikes = (int)$result2->num_rows;
?>
                        <span><?php echo $totalLikes; ?></span>
            </a>

            Now that like button calls a javascript script on the bottom of my page :

            <script>
                $("#addLike").on("click", function() {
                    var id_post = $(this).attr("data-id");
                    $.post("includes/handlers/addlike.php", {
                        id: id_post
                    }).done(function(data) {
                        var result = $.trim(data);
                        if (result == "ok") {
                            location.reload();
                        } else {
                            console_log(result);
                        }
                    });
                });
            </script>