The team also added center Greg Eslinger and cornerback Rashod Moulton to the practice squad.
The moves were announced Monday.
Jackson was released by New England in late August after two seasons. He has 13 catches, 152 yards and three touchdowns in 14 games.
Buffalo released Murphy Sept. 13. He has played in 28 games at tackle and tight end in Buffalo, Houston and Detroit.
Bell had been on Denver's practice squad for five weeks.
This is Eslinger's second stint with the Broncos, who drafted him in the sixth round in 2006.