I have the wallet.dat file here but when downloaded the Bitcoin Core wallet and synched it and then overwrote the wallet.dat with the new one it came up with a balance of 0. Am I doing something wrong or missing something?
Core does never overwrite a wallet.dat if it already exists in the directory.
Chances are high that this is your old wallet (if it was in the correct directory).
Core does only create a new wallet.dat if there is no in the data directory (standard directory?)
Even if you have deleted the file, under some circumstances you would be able to recover it using some recovery tool and a linux distro.
But, the phrase from your OP is not related to core in any way (maybe your wallet password?).