Communication plan

First is important to note that ISO 22301 nor ISO 27001 do not prescribe how a communication plan must be documented, so it is up to the organization to decide if it will be a separated document or not. 

For small and medium size organizations we understand that a separated document would increased administrative effort unnecessarily, so information related to communication plan is available in the several templates, for example:
- Disaster recovery plan, located on folder 08 Annex A >> A.17 Business Continuity >> 04 Business Continuity Plan
- Activity recovery plan, located on folder 08 Annex A >> A.17 Business Continuity >> 04 Business Continuity Plan

- Information Security Policy, located on folder 04 Information Security Policy
-  Incident management, located on folder 08 Annex A >> A.16 Incident Management 

In each document information related to communication is defined according the document purpose.