The contract will pay Robertson $10 million in 2019, $11 million in 2020, and includes a team option worth $12 million with a $2-million buyout option for 2021, according to Mark Feinsand of MLB.com.
Robertson, 33, posted a 3.23 ERA and 2.97 FIP over 69 2/3 innings out of the New York Yankees' bullpen last year. The one-time All-Star also recorded 19 saves and blew six over the last two seasons while pitching mostly in a setup role as part of New York's elite reliever group.
In each of the previous nine campaigns, the right-hander's worked at least 60 innings in relief, authoring a 2.72 ERA and 2.75 FIP over that span with 136 saves.
He now joins a Phillies bullpen that includes 2018 breakout reliever Seranthony Dominguez along with veterans Tommy Hunter and Pat Neshek. The club was also reportedly interested in signing Andrew Miller, who wound up inking a two-year deal with the St. Louis Cardinals.
Overall, Philadelphia's bullpen posted a pedestrian 4.19 ERA and 3.95 FIP in 2018, which ranked 11th and ninth, respectively, among National League teams.