Taxable amount on 1099-R distribution

On the 1099-R I just received from an my annuity company the Taxable amount (Box 2a) is much less than the Gross distribution amount (Box 1). Also, box 5 shows the amount of difference between the gross and taxable amounts. When I enter these amounts in Turbo Tax it is still showing that the taxable amount for income tax purposes is the higher amount in the Gross distribution box. My annuity company told me that the smaller amount in the taxable amount box is what I owe. This is because most of what was distributed to me in 2019 was out of my cost basis not the earnings from my investment. Why is TT still showing the gross amount instead of the taxable amount for income tax purposes?