It seems to be part of an investigation into his fundraising:
https://abc7ny.com/eric-adams-nyc-mayor-fbi-phones-campaign/14040894/Sources said investigators came to the mayor after the event on Monday to ask for all devices he had on his person, including an iPad and a phone
Later, the mayor's office turned over more devices. Most of the devices have been returned.
Adams has said he will fully cooperate with investigators who raided the home of the chief fundraiser for his 2021 campaign.
The investigation is exploring whether his campaign received illegal donations.
The focus of the investigation is if a Williamsburg construction company and a group of Turkish nationals may have made improper donations to the mayor's 2021 election campaign.
It also seems to be connected to a straw donor case and the former city buildings commissioner basically trading cash for favours:
Back in July, four people were charged in a scheme to raise money through straw donations for Adams' campaign. The defendants then intended to pressure the mayor's office for construction jobs.
Adams wasn't charged and a campaign spokesman said then "we would never tolerate these actions."
The former city buildings commissioner under Adams, Eric Ulrich, was also charged in September with using his position to dole out favors, including access to the mayor, in exchange for cash and other bribes.
Adams has distanced himself from both cases, which were brought in state court and did not directly implicate his campaign or administration.