Office of Personnel Annuity Question

This is the first year that I have to take over my father's taxes.  He has a statement of annuity paid 1099-R from the Office of Personnel Management.  The taxable amount in 2A is UNKNOWN.  It has a number in box 9B.  What am I supposed to do in this situation.  He had a CPA do his taxes last year, but they just left the 2b blank, which doesn't seem right.  I know my sister had to mail in his 1099-R to the IRS, as they had questions last year.  It seems I have to do the "simplified method", but I don't have the date and year the annuity started, or the plan cost on the start date to do the calculations.  I have repeatedly asked OPM for this data, but their phone line just hangs up saying they are too busy.  I have tried repeatedly for several days and tried to get a hold of them, but no use.  I have filled out the form to ask them a question and got a response, but the response is always talk to the IRS we don't do taxes.  I asked them specifically for the start date and the plan cost, but they are just sending me a statement of his annuity, which I already know.  I tried within Turbotax to fill out the worksheet with the simplified method to the best of my ability, but it keeps questioning the fact that the 2A box is left blank.  What should I do?