The outline phase seeks to establish the scope of the solution before spending (too much) time on details.
In smaller project one iteration is usually enough. For large and complex solutions it can make sense to split the outline phase in multiple iterations, each with a specific theme.
One such theme could be operations, which is often overlooked, and is rarely of interest to the so-called ‘business’.
Other obvious themes could be various areas of the business.
In addition to general refinements the risk and problem lists should be updated.
Detail the necessary activities and required resources.
Start listing business rules as the business process and information models are outlined.
To verify technology choices and release capabilities, this phase should deliver at least one release. While business requirements are still sketchy (being outlined, not detailed yet) the solution architect and developers need to tackle initial technical risks before the project starts the detail phase.
Finish the phase with an iteration report that lists achievements and lessons learned.