Box 2 on my 1098 is blank. It's not a 1098T. The annual tax and interest statement shows the outstanding mortgage amount. Should I enter that amount in box 2?

Yes, except you'll enter the beginning balance, not what it was at the end of the year.  Box 2 on the 1098 Mortgage Interest Statement is for the outstanding mortgage principal balance as of January 1st of that tax year, or if you acquired your mortgage at some point during the year, that box could be blank... In this case you would just need to "enter the outstanding mortgage principal as of the date of acquisition".

Below is from the IRS tax site. <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/i1098.pdf">https://www.irs.gov/pub/irs-pdf/i1098.pdf</a>

Box 2. Outstanding Mortgage Principal - Enter the amount of outstanding principal on the mortgage as of January 1, 2018. If you originated the mortgage in 2018, enter the mortgage principal as of the date of origination. If you acquired the mortgage in 2018, enter the outstanding mortgage principal as of the date of acquisition.