I believe the Design Phase for SDLC is very important for QA because the design phase identifies the potential risks. Knowing what is needed to be fixed helps focus on the issue to resolve it.

QA is critical for both business and the end user to prevent any defects of bugs in any system or software. This is beneficial for the business to keep it running smoothly without any setbacks also for the end user to do their job as a QA and do it correctly to keep the flow of operation with less or any errors on their end, so both parties are satisfied.