You can give a try to TinyPNG PHP library. Using this library your image gets optimized automatically during resizing process. All you need to install the library and get an API key from https://tinypng.com/developers. To install a library, run the below command.
composer require tinify/tinify
After that, your code is as follows.
require_once("vendor/autoload.php");
\Tinify\setKey("YOUR_API_KEY");
$source = \Tinify\fromFile("large.jpg"); //image to be resize
$resized = $source->resize(array(
"method" => "fit",
"width" => 150,
"height" => 100
));
$resized->toFile("thumbnail.jpg"); //resized image
I have a written a blog on the same topic http://artisansweb.net/resize-image-php-using-tinypng