Let me know if this helps, and if you run across anything else be sure to check out the QuickBooks Learn and Support page for more great how-tos and articles. Don't hesitate to leave a reply below, I'm always happy to further assist.
The option to sort the purchase orders when adding them to a bill is unavailable. The system sorts the POs by date so you can see the recent ones you've entered. Just select the PO to add on the bill based on the number you set to it.
Feel free to use these links to help you manage your vendor transactions: