diff --git a/lib/modules/manager/composer/utils.spec.ts b/lib/modules/manager/composer/utils.spec.ts
index 5cb469118628f914f86012994264c2457702d2ad..4f2e0fd5ff76aa3a10f3a8cce4a356888044b45b 100644
--- a/lib/modules/manager/composer/utils.spec.ts
+++ b/lib/modules/manager/composer/utils.spec.ts
@@ -27,7 +27,55 @@ describe('modules/manager/composer/utils', () => {
           },
           {}
         )
-      ).toEqual({ composer: '1.*', php: '7.4.27' });
+      ).toEqual({ composer: '1.*', php: '<=7.4.27' });
+    });
+
+    it('returns platform 0 minor php version', () => {
+      expect(
+        extractConstraints(
+          {
+            config: { platform: { php: '7.0.5' } },
+            require: { php: '^7.0 || ~8.0' },
+          },
+          {}
+        )
+      ).toEqual({ composer: '1.*', php: '<=7.0.5' });
+    });
+
+    it('returns platform 0 patch php version', () => {
+      expect(
+        extractConstraints(
+          {
+            config: { platform: { php: '7.4.0' } },
+            require: { php: '^7.0 || ~8.0' },
+          },
+          {}
+        )
+      ).toEqual({ composer: '1.*', php: '<=7.4.0' });
+    });
+
+    it('returns platform lowest minor php version', () => {
+      expect(
+        extractConstraints(
+          {
+            config: { platform: { php: '7' } },
+            require: { php: '^7.0 || ~8.0' },
+          },
+          {}
+        )
+      ).toEqual({ composer: '1.*', php: '<=7.0.0' });
+    });
+
+    it('returns platform lowest patch php version', () => {
+      expect(
+        extractConstraints(
+          {
+            config: { platform: { php: '7.4' } },
+            require: { php: '~7.4 || ~8.0' },
+          },
+          {}
+        )
+      ).toEqual({ composer: '1.*', php: '<=7.4.0' });
     });
 
     it('returns from require-dev', () => {
diff --git a/lib/modules/manager/composer/utils.ts b/lib/modules/manager/composer/utils.ts
index 166d4c5ee74924f64cf79c54f561cf98e8418b23..3571196ad30ae71abd787cdcc94c624bc9bcccb9 100644
--- a/lib/modules/manager/composer/utils.ts
+++ b/lib/modules/manager/composer/utils.ts
@@ -75,7 +75,10 @@ export function extractConstraints(
 
   // extract php
   if (composerJson.config?.platform?.php) {
-    res.php = composerJson.config.platform.php;
+    const major = api.getMajor(composerJson.config.platform.php);
+    const minor = api.getMinor(composerJson.config.platform.php) ?? 0;
+    const patch = api.getPatch(composerJson.config.platform.php) ?? 0;
+    res.php = `<=${major}.${minor}.${patch}`;
   } else if (composerJson.require?.php) {
     res.php = composerJson.require.php;
   }