The Design Phase is the process of turning the proposed solution into something developers can build. Accelerated timelines often begin in this phase… which is acceptable if the iteration cycle is tight.
Any solution proposed without a Discovery and Ideation Phases is nothing more than a guess. In software development, guesses must be validated with users early and often. Trying to work solely in the Design Phase is a recipe for failure and I do not recommend it.
In my experience, the output of this phase will vary from project to project. I’ve worked in collaborative environments as well as “throw it over the fence” environments. The UX vision is often dependent on developers, so knowing what the dev teams require is the key to having a successful Design Phase.