You don't is the simple answer. There are no phases. There is already an assumption that the project is two years. This is incorrect, you should only recognize that you have 2 years of budget to fund a project.
Agile scrum teams schedule 5 things: standups, plannings, reviews, retrospectives, and iterations. You could schedule a scrum team with 2 week iterations to have about 50 iterations over 2 years.
Realistically, the project schedule is unknown to you. Fund the team that will work on the project. Assuming it is a scrum team, the product owner, working directly with the customer, is responsible for generating the product backlog and prioritizing it. This will result in an initial product roadmap that identifies in which order business valuable features will be iteratively delivered to the customer. The initial roadmap will not tell you the duration of the project.
As mentioned in another post, fund the team's operation for around 3 iterations to establish an initial velocity. Using the team velocity it is possible to start generating a very rough forecast of the project duration assuming the backlog is fully built out and all items are roughly estimated. In this instance, if the forecast is +/- 6 months of the 2 years of budget thats pretty healthy. If not, this is your first hint that its time to start doing some expectation management or risk mitigation. This is when Agile stakeholders also learn that Agile project "schedules" are living documents that should change frequently.
So this is the project "schedule." It should now communicate the order and rough timing in which the team thinks it can deliver value.
This Agile "schedule" is not a commitment. It is a forecast and the customer/stakeholders should understand the assumptions and variability in the forecast.
The concept of a Waterfall project schedule is gone, since it is unrealistic to think that a 2 year plan will materialize as planned two years down the road.
Iterative delivery, smaller feedback loops, and building customer trust replace the project schedule on truly Agile teams.
"But wait! My two years is based on a fixed scope/budget agreement with the customer!" Its time to recognize the risk that the rest of your organization is still operating in a waterfall mindset and the friction between the two methodologies will probably produce mediocre results.
For Agile methodologies like scrum to provide maximum benefit, they need to be adopted throughout the org, not just at the delivery team level.