The Playoff Roster screen is only available during the playoffs, and only when the currently selected team is in the playoffs. This where you can manage the playoff roster of the selected team:

The Player Trade Status sub-screen behaves very similarly to the Overview page, except that by default the top left shows the team's Playoff Roster. The bottom left shows the active roster. The top right shows players who are eligible for the playoff roster, and the bottom right shows a list of rules for who is eligible for the playoff roster.

See Playoff Rosters for more information.