The relationship between the portfolio management plan and the communication plan is that the communication management plan:

According to PMI's Standard for Portfolio Management, the portfolio management plan is the master planning document that encompasses multiple subsidiary plans, including the communications management plan. This hierarchical relationship means communication planning is governed within the broader portfolio management planning framework. The portfolio management plan is developed first, and subsidiary plans like the communication plan are created as components within it.

The communication management plan is a subsidiary plan within the portfolio management plan and does not serve as the overarching driver of portfolio communications governance.

The communication management plan and portfolio management plan are not at the same level or independent; the former is a subsidiary of the latter.

The portfolio management plan is developed before its subsidiary plans, including the communications plan, not the other way around.