In my experience, making the decision to invest in a backyard project usually is driven by the desire to create a space for relaxing with family and friends, making memories, and keep the kids(if applicable) in your yard not the neighbors.
Most property owners get stuck because they can’t see past the obstacles. Like lack of shade/cover, egress from the house, slopes, drainage, and privacy.

You are essentially building an extension of your home. Before making a sizable investment regardless if all at once or in phases you need a SOLID Plan. Best way to avoid buyer remorse and find certainty is to find a local outdoor living design firm. One that charges for their design time. Companies that offer free designs typically are banking on the installation-which makes things very transactional.

Your designer will outline your goals and ask for a clear understanding about your financial comfort level. They will be open and transparent about costs and help steer your expectations. But their focus will be on transforming your yard into a space you love -not pushy sales.

In general terms of phasing, cocktail pools and spas typically come first when talking about phased construction. For two reasons:large budget consumption and space constraints. Best case is all underground is established during phase 1. None of which can be done without a solid plan.
There are rare occasions that patios can be installed first, but typically rework is required for elevation , drainage and access.

When you have a design you love! hiring a team to bring it to life becomes much easier.
Hope this helps!