Filter Choice Controlling Other Filters

1. Ensure Proper Data Model Design
You need a structure where both Phase and Study belong to the same table, or they are properly related.
Alternatively, if you have dimension tables:
PhaseDim (PhaseID, PhaseName)
StudyDim (StudyID, StudyName, PhaseID)
Then ensure:
StudyDim[PhaseID] is related to PhaseDim[PhaseID]
Your fact table has StudyID, which connects to StudyDim[StudyID]

2. Add Slicers
Add a slicer for Phase
Add another slicer for Study
Power BI will automatically filter the Study slicer based on the selected Phase if the model relationships are correct.

3. Ensure Relationships Are Set to "Single" Direction
Go to Model View and ensure:
Relationships between Phase → Study are set to Single directional filtering (from Phase to Study or from Study to Fact).
Avoid bidirectional relationships unless absolutely needed.

4. Avoid Adding Filters from Unrelated Tables
If your slicers come from unrelated tables, cascading will not work. Make sure the filter field sources are properly related either directly or through a fact table.