iPhone 6 (with Safari):

"Request Total" appears after holding the "Refresh" button in Safari, and selecting "Request Desktop Site"

Summary:

So as someone further up said - the phone browser needs to be set to desktop using the appropriate method; the only browser it doesn't work in is Samsung Internet.

I wish eBay would just fix it. The instructions on my listings for combining postage are already lengthy enough, without having to add the above instructions.