Using sub-summary data in a calculation

I have the following raw table data:

Days      Phase

2              1

10           1

23           2

3              1

4              3

I can create a sub-summary report to total of all the days by phase:

Days      Phase

15           1

23           2

4              3

My question: How do I write the formula to use these sub-summary totals in a calculation?

Example:

Total number of phase 1 days * 2 = 30

Thanks,

David