The federal income taxes withheld on your W-2 (Box 2) is an estimate that you and your employer made at the beginning of the year (when you filed your W-9 with your employer) of how much federal income tax you would owe.
Now we are at the end of the year, and you have entered all your information into TurboTax, and the software has calculated what you actually owe.
As you can imagine, the estimate for your W-2 and your spouse's are likely different. Furthermore, as you add income to the Family, the effective tax rate rises, so what would have been a good estimate for one W-2 may not not a good estimate for both W-2s.
Your estimate on the W-2 is almost certainly high or low. If your estimate was high, then you will likely get a refund. If you estimate is low, you will likely owe tax.
The number in Box 2 is not the amount of tax that the IRS assesses but only how much was withheld to pay for your assessed tax.