The midfielder will sign a three-year deal with the U's on July 1 after joining from Championship side Blackpool on a free transfer.
"Paul Lambert (manager) sold the club to me and outlined his plans which are to win games," Fox told BBC Essex. "The ambition is to go up and I don't see this as a backward step."
The former Manchester United trainee was out of contract with Blackpool when Lambert stepped in to snap him up.
"I used to room with Darren Fletcher at United and played with Kieran Richardson and Chris Eagles and I'm looking to progress with my career as they have," Fox added.