How to upload photos from the photo library to eBay

I am an eBay seller and use photos taken using my iPhone to illustrate my sales.

iPhone images import automatically to the photos app and are visible in the photo library.

If I create my ad on eBay and arrive at the add photos stage, the photo library is 'greyed out' and inaccessible. Therefore I can no longer upload images to eBay.

Does anyone know how to resolve this issue?