Game concept
Scheme Phase
The game also links it as Scheme Phases, Phase, Phases.
From the game's encyclopedia
A Phase is the length of time it takes to boost Scheme Success Chance once.
Each Phase the Scheme will gain an Advantage. The Phase Length can be shortened by appointing Agents, and is increased by the Scheme Resistance of the target.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Scheme Phase is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Phase is the length of time it takes to boost Scheme Success Chance once." It is part of Scheme. The game also links it as Scheme Phases, Phase and Phases. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.