The regular standard deduction is not phased out by your income. Since both you and your spouse are over 65, that would be the regular standard deduction for a couple that is filing a joint return with both people over 65.
The senior bonus deduction is what is phased out due to income is over $250,000, the BONUS would be fully phased out, but not the regular standard deduction.
As long as line 13b is $0 then this is correct.
The additional amount is the extra $1,600 for each of you that is part of the standard deduction. This is NOT affected by your income.