It shouldn't increase your taxable income, it may increase your overall "income" on the summary screen but that doesn't make it taxable. An after-tax retirement plan is not actually a "Roth" IRA although they are similar in purpose. If this was a direct transfer from plan-to-plan, it should have a code G (or maybe H) in box 7 which would automatically make it non-taxable, but you still enter it. If you got a check, it would be code J, and then you have to tell the IRS that it was rolled over to a new qualifying plan within 60 days.
@dmertz
