As You can see they told already that the priv key is a "big integer" so basically it is not a sha256 hash in my opinion.
So you think it would be a "big integer" in base10? A private key in base10 would have to be 77 characters long. Any ideas for combining a 21 digit number and a 27 digit number to end up with a 77 digit number?
To be honest I don't really see any other way that can we convert those words for exactly 27-digit number.
If you see
my post above, all the characters of "Phemex", "BTC", "ETH", and "XRP" are present in Base58Check encoding, which is the method used to encode WIF private keys. This encoding also misses out the letters "I" and "O", since they are easily confused with lower case "L" and number zero, which could be the answer to the clue "Without I/O".