The Office of the Director of National Intelligence publicly released the redacted report following a Freedom of Information Act lawsuit by the New York Times.
The basics of the National Security Agency program had already been declassified, but the lengthy report includes some new details about the secrecy surrounding it.
President George W Bush authorised the "President's Surveillance Program" as part of the Patriot Act in the aftermath of the terrorist attacks on September 11, 2001.
They found that while many senior intelligence officials believe the program filled a gap by increasing access to international communications, others including FBI agents, CIA analysts and managers "had difficulty evaluating the precise contribution of the PSP to counterterrorism efforts because it was most often viewed as one source among many available analytic and intelligence-gathering tools in these efforts."
More From This Section
Critics of the phone records programme, which allows the NSA to hunt for communications between terrorists abroad and US residents, argue it has not proven to be an effective counterterrorism tool.
The Patriot Act expires on June 1, and Senate Republicans have introduced a bill that would allow continued collection of call records of nearly every American. The legislation would reauthorize sections of the Patriot Act, including the provision under which the NSA requires phone companies to turn over the "to and from" records of most domestic landline calls.
After the programme was disclosed in 2013 by former NSA contractor Edward Snowden, President Barack Obama and many lawmakers called for legislation to end that collection, but a bill to do so failed last year. Proponents had hoped that the expiration of the Patriot Act provisions on June 1 would force consideration of such a measure.