Is it correct, that if I select an entry in Phase 1, all Phase 2 entries, including those from other Phase 1 entries, will be displayed?
No it should filter Phase 2 based on Phase 1 selection.
This fixes the issue:
# opnsense-patch https://github.com/opnsense/core/commit/3ba41cc5b05a762ec9b26e99ec12a74c0039888a