The project planning phase may involve market evaluation, estimates of ROI, and whatnot. Engineering department is rarely involved in that and usually sees only a part of the overall planning.
As far as engineering department is concerned, the goal of the planning phase is to resolve Project management triangle—i.e., to define scope, time, and cost in which project can be delivered with a reasonable quality. Once the project is approved, engineering department is responsible to deliver on these constraints (Estimates in project planning phase tend to become deadlines).
Engineers rarely get access to cost figures but time × number of developers is a useful cost proxy.