Which actions are considered to watch for a specified step or phase to begin?

Triggered abilities are the correct answer because they specifically activate in response to certain game events, which include the beginning of a step or phase. These abilities are designed to "trigger" when specific conditions are met, such as the start of a particular phase or when a player plays a spell. For example, if a card has an ability that triggers at the beginning of your upkeep, it will automatically go on the stack when that phase begins.

In contrast, continuous effects modify the game state and remain in effect without needing to trigger anew; they do not specifically "watch" for when a phase begins. Turn-based actions are defined actions that players must carry out during their turn and do not involve triggered conditions. Static abilities provide ongoing effects but are not activated by the beginning of phases or steps—a distinction crucial in understanding how different game elements interact with the game timeline.