Essentially, this is the phase of Jack Smith's investigation that looks at Trump's document theft and crimes and/or criming related to this theft.
On June 8, 2023, Trump was indicted on 31 separate counts relating to the mishanding of national defense documents. He was charged under the Espionage Act for "gathering, transmitting or losing defense information, which also includes refusal to return information that is demanded by the government."
https://www.cbsnews.com/news/espionage-act-trump-mar-a-lago-fbi-search-warrant/

