diff --git a/get-shit-done/bin/lib/phase.cjs b/get-shit-done/bin/lib/phase.cjs
index 4df2beb60..ecde4d5c8 100644
--- a/get-shit-done/bin/lib/phase.cjs
+++ b/get-shit-done/bin/lib/phase.cjs
@@ -736,13 +736,20 @@ function cmdPhaseComplete(cwd, phaseNum, raw) {
         return '|' + cells.join('|') + '|';
       });
 
-      // Update plan count in phase section
+      // Update plan count in phase section.
+      // Use direct .replace() rather than replaceInCurrentMilestone() so this
+      // works when the current milestone section is itself inside a <details>
+      // block (the standard /gsd-new-project layout). replaceInCurrentMilestone
+      // scopes to content after the last </details>, which misses content inside
+      // the current milestone's own <details> wrapper (#2005).
+      // The phase-scoped heading pattern is specific enough to avoid matching
+      // archived phases (which belong to different milestones).
       const planCountPattern = new RegExp(
         `(#{2,4}\\s*Phase\\s+${phaseEscaped}[\\s\\S]*?\\*\\*Plans:\\*\\*\\s*)[^\\n]+`,
         'i'
       );
-      roadmapContent = replaceInCurrentMilestone(
-        roadmapContent, planCountPattern,
+      roadmapContent = roadmapContent.replace(
+        planCountPattern,
         `$1${summaryCount}/${planCount} plans complete`
       );
 
diff --git a/tests/bug-2005-phase-complete-details.test.cjs b/tests/bug-2005-phase-complete-details.test.cjs
new file mode 100644
index 000000000..7a98d0e2b
--- /dev/null
+++ b/tests/bug-2005-phase-complete-details.test.cjs
@@ -0,0 +1,180 @@
+/**
+ * Regression tests for bug #2005
+ *
+ * When the in-progress milestone section is wrapped in a <details> block
+ * (the standard /gsd-new-project layout), phase complete silently skips:
+ * 1. The plan count update (**Plans:** N/M → X/M plans complete)
+ * 2. Mis-reports is_last_phase and next_phase
+ *
+ * Root cause: replaceInCurrentMilestone() uses the last </details> as the
+ * boundary, so when the current milestone is itself inside <details>, the
+ * replacement target is in the empty space AFTER the current milestone's
+ * closing </details>, and the regex never matches anything inside the block.
+ */
+
+'use strict';
+
+const { describe, test, beforeEach, afterEach } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+const os = require('node:os');
+const { execFileSync } = require('node:child_process');
+
+const gsdTools = path.resolve(__dirname, '..', 'get-shit-done', 'bin', 'gsd-tools.cjs');
+
+describe('bug #2005: phase complete updates plan count when milestone is inside <details>', () => {
+  let tmpDir;
+  let planningDir;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gsd-2005-'));
+    planningDir = path.join(tmpDir, '.planning');
+    fs.mkdirSync(planningDir, { recursive: true });
+
+    fs.writeFileSync(
+      path.join(planningDir, 'config.json'),
+      JSON.stringify({ project_code: 'TEST' })
+    );
+
+    fs.writeFileSync(
+      path.join(planningDir, 'STATE.md'),
+      '---\ncurrent_phase: 1\nstatus: executing\nmilestone: v2.0\n---\n# State\n'
+    );
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test('plan count is updated when current milestone is wrapped in <details>', () => {
+    // This is the standard /gsd-new-project layout: every milestone in <details>
+    const phasesDir = path.join(planningDir, 'phases', '01-setup');
+    fs.mkdirSync(phasesDir, { recursive: true });
+    fs.writeFileSync(
+      path.join(phasesDir, '01-1-SUMMARY.md'),
+      '---\nstatus: complete\n---\n# Summary\nDone.\n'
+    );
+    fs.writeFileSync(
+      path.join(phasesDir, '01-1-PLAN.md'),
+      '---\nphase: 1\nplan: 1\n---\n# Plan 1\n'
+    );
+
+    const roadmapPath = path.join(planningDir, 'ROADMAP.md');
+    // Current milestone (v2.0) is wrapped in <details>
+    fs.writeFileSync(roadmapPath, [
+      '# Roadmap',
+      '',
+      '<details>',
+      '<summary>v1.0 (shipped)</summary>',
+      '',
+      '## v1.0 Phases',
+      '- [x] **Phase 0: Bootstrap** - shipped',
+      '',
+      '</details>',
+      '',
+      '<details open>',
+      '<summary>v2.0 (in progress)</summary>',
+      '',
+      '## v2.0 Phases',
+      '',
+      '- [ ] **Phase 1: Setup** - initial setup',
+      '- [ ] **Phase 2: Build** - build features',
+      '',
+      '## Progress',
+      '',
+      '| Phase | Plans | Status | Completed |',
+      '|-------|-------|--------|-----------|',
+      '| 1. Setup | 0/1 | Pending | - |',
+      '| 2. Build | 0/1 | Pending | - |',
+      '',
+      '### Phase 1: Setup',
+      '',
+      '**Plans:** 0/1 plans complete',
+      '',
+      '### Phase 2: Build',
+      '',
+      '**Plans:** 0/1 plans complete',
+      '',
+      '</details>',
+    ].join('\n'));
+
+    try {
+      execFileSync('node', [gsdTools, 'phase', 'complete', '1'], { cwd: tmpDir, timeout: 10000 });
+    } catch {
+      // May exit non-zero if STATE.md update fails, but ROADMAP.md update is the target
+    }
+
+    const result = fs.readFileSync(roadmapPath, 'utf-8');
+
+    // Plan count must be updated inside the <details> block
+    assert.match(
+      result,
+      /\*\*Plans:\*\*\s*1\/1 plans complete/,
+      'plan count in Phase 1 section must be updated to 1/1 plans complete'
+    );
+
+    // Phase 1 checkbox must be checked
+    assert.match(
+      result,
+      /- \[x\] \*\*Phase 1: Setup\*\*/,
+      'Phase 1 checkbox must be checked after completion'
+    );
+
+    // Phase 2 must be untouched
+    assert.match(
+      result,
+      /- \[ \] \*\*Phase 2: Build\*\*/,
+      'Phase 2 checkbox must remain unchecked'
+    );
+  });
+
+  test('phase complete with all milestones in <details> does not corrupt phase 2 plan count', () => {
+    const phasesDir = path.join(planningDir, 'phases', '01-setup');
+    fs.mkdirSync(phasesDir, { recursive: true });
+    fs.writeFileSync(
+      path.join(phasesDir, '01-1-SUMMARY.md'),
+      '---\nstatus: complete\n---\n# Summary\nDone.\n'
+    );
+    fs.writeFileSync(
+      path.join(phasesDir, '01-1-PLAN.md'),
+      '---\nphase: 1\nplan: 1\n---\n# Plan 1\n'
+    );
+
+    const roadmapPath = path.join(planningDir, 'ROADMAP.md');
+    fs.writeFileSync(roadmapPath, [
+      '# Roadmap',
+      '',
+      '<details open>',
+      '<summary>v2.0 (in progress)</summary>',
+      '',
+      '## v2.0 Phases',
+      '',
+      '- [ ] **Phase 1: Setup** - initial setup',
+      '- [ ] **Phase 2: Build** - build features',
+      '',
+      '### Phase 1: Setup',
+      '',
+      '**Plans:** 0/1 plans complete',
+      '',
+      '### Phase 2: Build',
+      '',
+      '**Plans:** 0/2 plans complete',
+      '',
+      '</details>',
+    ].join('\n'));
+
+    try {
+      execFileSync('node', [gsdTools, 'phase', 'complete', '1'], { cwd: tmpDir, timeout: 10000 });
+    } catch {}
+
+    const result = fs.readFileSync(roadmapPath, 'utf-8');
+
+    // Phase 2's plan count must NOT be touched
+    assert.match(
+      result,
+      /Phase 2: Build[\s\S]*?\*\*Plans:\*\*\s*0\/2 plans complete/,
+      'Phase 2 plan count must remain 0/2 (untouched)'
+    );
+  });
+});