I'm having problems mastering the phase 2. What should I do?

Patience. I would recommend completing both phase 1 and phase 2 again. Phase 2 is not a walk in the park and mastering the exercises should take time. Jumping to the phase 3 before mastering phases 1 & 2 is not a good idea.

The better you master each phase, the better results you can expect. Although each phase is a 4-week program, the program can and should be repeated as many times as necessary.