Read full tutorial here : https://cedricleruth.com/how-to-upload-a-folder-contents-to-aws-s3-in-php/

UploadLocalFolderContentToAwsS3.php

<?php

// Include AWS php sdk that you can download here : https://docs.aws.amazon.com/sdk-for-php/v3/developer-guide/getting-started_installation.html
require 'aws/aws-autoloader.php';
use Aws\S3\S3Client;
use Aws\S3\Exception\S3Exception;

// Initialize your S3 connection. 
// To generate your YOUR_IAM_USER_KEY and YOUR_IAM_USER_SECRET create and Aws IAM user with the S3FullAccess Role 
// to do so follow : https://docs.aws.amazon.com/IAM/latest/UserGuide/id_users_create.html
$s3 = new Aws\S3\S3Client([
  'region' => 'YOUR_S3_REGION',
  'version' => 'latest',
  'credentials' => [
      'key'    => "YOUR_IAM_USER_KEY",
      'secret' => "YOUR_IAM_USER_SECRET",
    ]
  ]);

$dir = "/FULL_DIRECTORY_TO_UPLOAD_PATH/*";
//for example $dir = "/home/ubuntu/Projets/MY_PROJECT/MY_FOLDER_TO_UPLOAD/*";

//For each file in your directory run the putObject S3 Api function
foreach (glob($dir) as $file) {
    $file_name = str_replace('/FULL_DIRECTORY_TO_UPLOAD_PATH/', '', $file);
    echo "Upload File Key : ".$file_name . "\n";
    echo "Upload File Path : ".$file. "\n \n";
    $result = $s3->putObject([
        'Bucket' => 'YOUR_S3_BUCKET_NAME',
        'Key'    => 'FOLDER_NAME_INSIDE_S3_BUCKET/'.$file_name,
        'Body' => fopen($file, 'r+')
    ]);

    // Wait for the file to be uploaded and accessible :
    $s3->waitUntil('ObjectExists', array(
      'Bucket' => 'YOUR_S3_BUCKET_NAME',
      'Key'    => 'FOLDER_NAME_INSIDE_S3_BUCKET/'.$file_name
  ));
}