You can play (but not create) Scratch projects on most smartphones using the browser version of Scratch. You can also leave comments using your phone.
We don't currently have a Scratch app for smartphones. If you're using a Chromebook or Android tablet, you may be able to download our application on the Google Play store. Visit this link: https://play.google.com/store/apps/details?id=org.scratch to see if your device is compatible.