This activation phase is intended to stack stability around the newfound mobility. For that we're going to look to stabilize at the pelvis, trunk, and shoulder specifically.
Mobility with no stability is just a floppy mess. As you go through this phase of the warm-up, make sure to feel yourself activate (or contract) at points where stability is required. Here you'll do three movements, each with a specific area of activation:
Romanian Deadlift (glute activation): Don't rush through this movement. Feel yourself extend the hips fully at the top.
Squatting Muscle Snatch with Trap Raise (shoulder stability): To lock in shoulder stability, pull through a full range of motion and then press the bar with a trap raise at the top. This is also an awesome move for practicing good "tight bar" technique.
Overhead Squat (trunk activation): The last piece of activation is to work on stabilizing the trunk throughout the movements. Without trunk stability you won't be able to maintain position in the lifts. Now you could certainly hammer out some overhead squats without even thinking about having a stable trunk, so the key is to really focus on finding and maintaining stability.