In the application and negotiation phase
The dissemination activities may be part of the evaluation criteria defined in the work programme.
Usually communication and dissemination activities are evaluated as part of the impact of the project. Dissemination is mainly understood as scientific dissemination and communication as science communication into society.
Create a detailed "Dissemination and Exploitation Plan" as well as a "Communication Plan" already in the application phase!
During the negotiation phase, the EU Commission may ask you to improve and expand your activities in this field.