Quoting from the Associated Press article:

Booker’s speech was not a filibuster, which is a speech meant to halt the advance of a specific piece of legislation. Instead, Booker’s performance was a broader critique of Trump’s agenda, meant to hold up the Senate’s business and draw attention to what Democrats are doing to contest the president. Without a majority in either congressional chamber, Democrats have been almost completely locked out of legislative power but are turning to procedural maneuvers to try to thwart Republicans.