What are the various stages of a PhD. In terms of the proposed timeline?

That question is way too broad due to the high variability between students, projects, disciplines, countries and supervisors.

TreeofLife is right, the question is way too broad. I'm also not sure if you are interested in various 'official' stages, like initial period of study, intermediate viva, etc. or if you ask in terms of content/research plan only.
Try give us more details, I'm sure you'll get useful responses then.

Sorry if the questions appears too broad. It was asked by a prospective supervisor. I will seek to narrow the question.

Are you trying to write a project proposal?

You yourself can narrow the question by telling us more about the project (Science? Humanities? Qualitative/quantitative? Primary data collection or secondary analysis?)