Step 1: Understand the phases of production planning and control.
Production planning and control (PPC) involves various phases like planning, scheduling, and controlling the production processes.
Step 2: Identify where order writing fits.
- Order writing is part of the planning phase, where production orders are written and prepared to execute production. This phase involves planning for the materials, labor, and machinery required.
Step 3: Conclusion
Thus, order writing is included in the planning phase.
Final Answer:
\[
\boxed{\text{Planning phase}}
\]