How do I know if I should use phases or deliverables for my WBS? and what is the difference?

WBS is a key information for project, phases, milestone, and deliverable should be defined and highlighted. most of companies have a guideline to define projects control points. the approach to this may refer to financial, cash flow and contract terms, or due to the product itself, customer needs

you can use CPM to initiate control framework, define milestone based on contractor and execution process phases and deliverable based on technical inspection and formal review.