PHP $_POST empty -- not working for local server using MAMP

So currently, this is the code I have

index.php:

        <form action="insert.php" method="post">
            Comments:
            <input type="text" name="comment">
            <input type="submit">
        </form>

insert.php:

<?php

include ('index.php');

$user = 'x';
$password = '';
$db = 'comment_schema';
$host = 'localhost';
$port = 3306;

/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */

$link = mysqli_connect("localhost", "x", "", "comment_schema");

// Check connection
if($link === false){
   die("ERROR: Could not connect. " . mysqli_connect_error());
}

// Escape user inputs for security
$comment = mysqli_real_escape_string($link, $_POST["comment"]);
$sql = "INSERT INTO parentComment(ID, Comment) VALUES('','$comment')";

// attempt insert query execution
if(mysqli_query($link, $sql)){
   echo $comment;
} else{
 echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}

// close connection
mysqli_close($link);

When I do echo $comment, nothing gets printed out. However, if I do something like echo "hi" it works. I think for some reason the $_POST is not being recognized. Any suggestions to make this work or if I'm doing it wrong.

My goal is to take a user input and insert into a database on phpmyadmin. Currently, it is able to insert, however it inserts an empty value. I only have two columns in my database. An ID and a Comment column. The ID is auto incremented. The comment is what I get from the user.