Resize images uploaded after Ajax file upload
This is a common question. However it is out of the scope of phpGrid. The recommended way is to set up a Cron job that periodically triggers image resizing script (5 min, 10 interval you decide) with ImageMagick®.
ImageMagick is a free, open-source software suite, used for editing and manipulating digital images. It supports powerful command line scripts for bulk processing.
Here is a good tutorial explained quite well, let me know should you need help on that.
https://www.howtogeek.com/109369/how-to-quickly-resize-convert-modify-images-from-the-linux-terminal/
Another way for image resize upon upload is to add resize script after file upload in ajaxfileupload.php.