Which is the least risky phase of a project?

I would go with planning.

Risk level is highest towards the start of the project because there are many unknowns and uncertainties, as the work completes the unknowns become knowns and tasks are completed, towards the closing phase there is almost zero or little risk.

closing sure, check pmbok guide

stakeholder influence, risk and uncertainty are highest at the beginning.

As per my old post, you will have to trust PMP person like me. You would NEVER know the right answer PMP is looking for. Here is my perspective:

Business is all about money. Planning phase has least money involved because it’s all about making various baselines (scope, cost, time, risk, quality etc) and getting it approved. The worst case is the plan rejection, but this is iterative as you can re-plan your baselines as per PMBOK. Hence planning process should be least risky.

All other phases like initiation, execution, M&C, closing has huge impact on budgets. Many people might say its “Closing Phase”, but keep in mind during closing process all claim process comes in picture and it’s a huge gambling. Closing process also involves product acceptance, it’s again a very big risky task i.e. you are selling your product for which you have invested about 95% of project cost.