If your stack is still Private then you should first set its access permissions to Public (See How do I set access permissions?) so that you can view it on your phone without signing in.
You can then view your ePoster stack on your smartphone by scanning its QR code. This will open the ePoster in the browser on your smartphone. You can interact with it in the browser or choose to open it in the LTB App.
If you are in the editor the you will not see the QR code. You should first press the Close Editor button. This will then bring you to the summary screen which shows the QR code.