diff --git a/get-shit-done/bin/lib/phase.cjs b/get-shit-done/bin/lib/phase.cjs
index 2244b9f02..3bda6758b 100644
--- a/get-shit-done/bin/lib/phase.cjs
+++ b/get-shit-done/bin/lib/phase.cjs
@@ -341,11 +341,13 @@ function cmdPhaseAdd(cwd, description, raw, customId) {
       _dirName = `${prefix}${_newPhaseId}-${slug}`;
     } else {
       // Sequential mode: find highest integer phase number (in current milestone only)
+      // Skip 999.x backlog phases — they live outside the active sequence
       const phasePattern = /#{2,4}\s*Phase\s+(\d+)[A-Z]?(?:\.\d+)*:/gi;
       let maxPhase = 0;
       let m;
       while ((m = phasePattern.exec(content)) !== null) {
         const num = parseInt(m[1], 10);
+        if (num >= 999) continue; // backlog phases use 999.x numbering
         if (num > maxPhase) maxPhase = num;
       }
 
diff --git a/tests/phase.test.cjs b/tests/phase.test.cjs
index 38da0a662..4225be9a8 100644
--- a/tests/phase.test.cjs
+++ b/tests/phase.test.cjs
@@ -655,6 +655,43 @@ describe('phase add command', () => {
     const roadmap = fs.readFileSync(path.join(tmpDir, '.planning', 'ROADMAP.md'), 'utf-8');
     assert.ok(roadmap.includes('**Requirements**: TBD'), 'new phase entry should include Requirements TBD');
   });
+
+  test('skips 999.x backlog phases when calculating next phase number', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, '.planning', 'ROADMAP.md'),
+      `# Roadmap v1.0
+
+### Phase 1: Foundation
+**Goal:** Setup
+
+### Phase 2: API
+**Goal:** Build API
+
+### Phase 3: UI
+**Goal:** Build UI
+
+### Phase 999.1: Future Idea A
+**Goal:** Backlog item
+
+### Phase 999.2: Future Idea B
+**Goal:** Backlog item
+
+---
+`
+    );
+
+    const result = runGsdTools('phase add Dashboard', tmpDir);
+    assert.ok(result.success, `Command failed: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+    assert.strictEqual(output.phase_number, 4, 'should be phase 4, not 1000');
+    assert.strictEqual(output.slug, 'dashboard');
+
+    assert.ok(
+      fs.existsSync(path.join(tmpDir, '.planning', 'phases', '04-dashboard')),
+      'directory should be 04-dashboard, not 1000-dashboard'
+    );
+  });
 });
 
 // ─────────────────────────────────────────────────────────────────────────────