You can deposit SOL for trading fees on your Phantom wallet. If you don't have SOL yet, you can purchase SOL on an exchange and withdraw SOL to your Phantom wallet.
Click on the "Deposit" button located next to the button you connected your wallet with and choose the amount you want to deposit.
If you want to withdraw from Drift, click on "Withdraw" inside the same window you used to deposit and choose the amount you want to withdraw. Click the maximum you want to withdraw and confirm.