When solving complex problems you're taught to try and break up the one problem in to smaller ones. Solve enough problems and in time you have the solution to the greater one.
Constructing a building for example is much simpler when broken down in to very small components that are easy to understand and manage.
We've taken this philosophy and applied it to the 3 lifts where each lift is broken down in to 3 phases. Each phase is independent of each other in the sense they have a different purpose/intent and must be completed properly before moving on to the next phase.
Each lift begins with the same phase, we call this the PREPATORY phase. As you guessed it's all about preparing for the lift including breathing & bracing and setting your start position. Of course each lift is slightly different but essentially it's the foundation you set up that allows for a high quality rep. In fact we could argue that this phase is the most important phase where 80% of your effort needs to be focused and that if not executed correctly, the rest of your lift will most likely show signs of dysfunction.
The second phase (for the squat and bench) we call the ECCENTRIC CONTROL phase. We use the word control because it's a phase that finishes in a position where we need to transition into an explosive phase where accuracy matters - we refer to the speed/accuracy trade off when explaining this in more detail. By executing control we are able to replicate a consistent bar path and final bar position where we can transition in to the final phase which we call the CONCENTRIC EXPLOSIVE phase.
No brainer, the CONCENTRIC EXPLOSIVE phase is all about generating as much force as possible and accelerating the bar through to lockout.
Note that the the deadlift has the ECCENTRIC CONTROL and CONCENTRIC EXPLOSIVE swapped around.
There's a bit of info on how we break the lifts up in to phases. Our Powerlifting Fundamentals Course also covers this topic in greater detail. For more information on the course check out https://www.ruccisgym.com/powerlifting-course-fundamentals