This paper investigates how the multi-phase representation of real-time tasks impacts their implementation and the precision of the interference analysis in a multi-core context. In classical scheduling and interference analyses, tasks are represented as a single phase with a duration equal to their Worst-Case Execution Time (WCET) in isolation, annotated with their worst-case number of accesses. We propose a general formal definition of a task model in which tasks are represented as a sequence of such phases: the multi-phase model. We then provide a set of general correction criteria for the implementation of tasks represented in the multi-phase model, which is agnostic of the analysis method applied on the tasks. We also use the multi-phase model on an avionics case-study and study its impact on the interference analysis. Finally, we define a set of efficiency criteria using a statistical study of the most efficient multi-phase shapes.