A special master reviewing a trove of documents and electronic files seized in April from Michael D. Cohen, President Trump’s longtime lawyer and fixer, said on Monday that, at least so far, only a tiny fraction of the materials are protected by the attorney-client privilege, meaning that most can be used by the federal prosecutors who are conducting a wide-ranging criminal investigation into Mr. Cohen.

In a report submitted to Kimba M. Wood, the federal judge presiding over Mr. Cohen’s case in Manhattan, the special master, Barbara S. Jones, said that only 14 paper documents out of the 639 that she had looked at are privileged, or partly privileged, and would be withheld from the prosecutors’ inquiry. Of the 291,770 electronic files contained on two of Mr. Cohen’s cellphones and on one of his iPads, 148 are privileged and will be withheld if the judge approves, Ms. Jones said.

In April, Judge Wood appointed Ms. Jones, a former federal judge, to review the contents of eight boxes of documents and more than 30 cellphones, iPads and computer drives seized during raids on Mr. Cohen’s office, apartment and hotel room to determine which among the materials were protected by the attorney-client privilege.

Prosecutors have been eager to get their hands on the documents and data in order to pursue a stalled investigation into whether Mr. Cohen broke the law in various business dealings, including two hush-money payments he made to women who claim they had affairs with Mr. Trump.