One of their traders emailed me saying that for now the details of how much I'd paid in dollars would not be available via my HL account but they were looking into adding them.
In the meantime I was told that I could find the particulars of my trade, priced in dollars, on the London Stock Exchange website.
So I took a look and yes, the details of all trades for one day are available for every share that is dealt on the exchange. An investor will need to be able to identify their own trade. I'm hoping I can do so just by knowing the number of shares I bought and the time I did the trade (and hope that no one else had done anything too similar recently).
How do you find these dollar prices? You can simply type PHAU into the search at the top of the LSE site and its page will come up - half way down you'll find a box showing the five most recent trades.
If you want to see all the trades for that day then adjust the controls above the displayed trades.
It should look like this: