This record is part of the NARA collection, "NARA M1675. Alphabetical Index to Declarations of Intention of the U.S. District Court for the Southern District of New York, 1917-1950" provided by fold3.
According to the description, the numbers are used to order record copies of the originals from NARA. "The three digit-number on these index cards is the volume number. The other number is the Declaration of Intention number."
For a little more information about this collection and naturalization, see the fold3 Topic Page. Included on the topic page are instructions for how to order the Naturalization Records indexed in NARA M1675.
The good news is that it appears you can order these records online! Does seem that in addition to the details from the index, NARA asks you to provide some additional information about the subject such as their approximate date of birth, country of origin and residence details at the time of naturalization. It's not possible for me to tell if this additional information is optional or required.