The 31-year-old was 4-8 with a 5.80 ERA and a .310 opponents' batting average in 19 starts and two relief appearances last year.
During a demotion to the minors, he went a combined 0-5 with a 7.02 ERA in seven starts with Triple-A Lehigh Valley, Double-A Reading and Class A Lakewood.
Eaton was left off the postseason roster by the World Series champions.
"Based on where we are with our pitching staff and the fact that we feel comfortable with our depth, we wanted to give Adam every opportunity to pitch with another club, rather than wait until later in the spring when it gets more difficult," Phillies general manager Ruben Amaro said.
Eaton agreed in November 2006 to a $24.5 million, three-year contract that called for an $8.5 million this year. The deal included a $9 million player option for 2010 but, if exercised, allowed the team to void the option and pay a $500,000 buyout.
Any team can sign Eaton for the $400,000 minimum, with the Phillies paying the rest of what he is owed.
Eaton was 14-18 with a 6.10 ERA in two seasons with the Phillies. Opponents hit .305 against him.
Eaton is 68-63 lifetime with a 4.80 ERA in nine years with San Diego, Texas and the Phillies.