Elements inside a model group retain the phase created and phase demolished properties as other Revit elements do. This is important to keep in mind when creating a new instance of a model group.
When inserting an instance of a model group, the elements will be created based on the current view phase. For example, if the view phase is Existing, and you create a new instance of a model group, all elements inside the group will be set to Phase Created: Existing. The model group itself does not have a phase, only the elements grouped. Edit the group to verify the element[s] phase.
Set the view Phase Filter temporarily to None in order to see all elements regardless of their phase properties.