I'm glad you visited the QuickBooks Support page for this packing slip concern. I'd be more than happy to share some insights about this.
For now, the option to export packing slips or delivery notes is not yet available in the mobile application for QuickBooks. The application will let you export invoices instead.
If you want to export packing slips, you can print to download them as PDF files in a web browser. This is how it is done: