PHP 5 password_hash()

// this is code to execute the usernameCheck when function uniqueUsername() is triggered
if(isset($_POST["usernamecheck"])) {
  // do this once you have a database: include_once("php-includes/db_conx.php");
  $username = $_POST['usernamecheck'];
  // $sql = "SELECT id FROM users WHERE username='$username' LIMIT 1";
  // $query = mysqli_query($db_conx, $sql);
  // $uname_check = mysqli_num_rows($query);
  $uname_check = 0; // this is for fun to test code until database is up
  if(strlen($username) < 5 || strlen($username) > 18) {
    echo '<strong style="color:#F00;">must be 5-18 characters long.</strong>';
    exit();
  } else if (is_numeric($username[0])) {
    echo '<strong style="color:#F00;">First character in username must be a letter.</strong>';
    exit();
  } else if ($uname_check < 1) {
    echo '<strong style="color:#009900;">This username is available!</strong>';
    exit();
  } else if ($uname_check > 0) {
    echo '<strong style="color:#F00;">This username is already taken.</strong>';
    exit();
  }
}
?><?php
if(isset($_POST["u"])) {
  // do this once you have a database: include_once("php-includes/db_conx.php");
  $username = preg_replace('#[^abcdefghijklmnopqrstuvwxyz0123456789_-]#i', "", $_POST['u']);
  $email = $_POST['e'];
  $cleanemail = filter_var($email, FILTER_SANITIZE_EMAIL);
  $password = $_POST['p'];
  // this will get the users ip address:
    // $ip = preg_replace('#[^0-9.]#', '', getenv('REMOTE_ADDR'));
  // this will check for same usernames:
    // $sql = "SELECT id FROM users WHERE username='$username' LIMIT 1";
    // $query = mysqli_query($db_conx, $sql);
    // $uname_check = mysqli_num_rows($query);
  // this will check for same email
    // $sql = "SELECT id FROM users WHERE email='$e' LIMIT 1";
    // $query = mysqli_query($db_conx, $sql);
    // $e_check = mysqli_num_rows($query);
  // handle code check for database return (using dummy var sets to make it work till data base is up)
  $uname_check = 0;
  $e_check = 0;
  if ($username == "" || $cleanemail == "" || $password == "") {
    echo "Your form is missing data.";
    exit();
  } else if ($uname_check > 0) {
    echo '<strong style="color:#F00;">This username is already taken.</strong>';
    exit();
  } else if ($e_check > 0) {
    echo '<strong style="color:#F00;">This email address is already in our system.</strong>';
    exit();
  } else if (is_numeric($username[0])) {
    echo '<strong style="color:#F00;">First character in username must be a letter.</strong>';
    exit();
  } else if(strlen($username) < 5 || strlen($username) > 18) {
    echo '<strong style="color:#F00;">Username must be 5-18 characters long.</strong>';
    exit();
  } else {
    // $p_hash = password_hash($password, PASSWORD_DEFAULT);
    // $sql = "INSERT INTO users (username, email, password, ip, lastlogin, signup) VALUES('$username', '$cleanemail', '$p_hash', '$ip', now(), now())";
    // $query = mysqli_query($db_conx, $sql);
    //if(!file_exixsts("user/$username")) {mkdir("user/$username", 0755);}
    $to = "$cleanemail";
    $from = "do_not_reply@sportsConnect.com";
    $subject = "SportSConnect Advertising Account Activation:";
    // surround message with '' so you can use double quotes within for html and 'around variables'
    //$message = 'Click this link to activate your account: <a href="http://www.sportsconnect.com/activation.php?id='.$uid.'&u='.$username.'&e='.$cleanemail.'&p='.$p_hash.'"Link</a>';
    $headers = "From: $from\n";
    $headers .= "MIME-Version: 1.0\n";
    $headers .= "Content-type: text/html; charset=iso-8859-1\n";
    if(mail($to, $subject, $message, $headers)) {
      echo 'wowo! the email is up and running!!!';
      exit();
    } else {
      echo 'good work';
      exit();
    }  
  }
}
?>```