... the general consensus is that the XLR connector is inherently superior to the RCA connector, balanced or not ...
I’ve seen some really exquisite RCA connectors but I’m inclined to agree with you - the XLR design is better from the get-go.
... "he" needs an XLR cable if he is plugging into a balanced phono that offers only XLR inputs.
The OP’s preamp takes has both RCA and XLR connectors on its input.