in5 can be used to create mobile-friendly web content from Adobe InDesign. There are 3 principal ways to test your content on mobile.

1) Post the files to a web server, then visit the URL on your device:

2) Use a local server (like MAMP) and a mobile simulator to test on your computer (somewhat complicated).

3) Use BrowserStack to test content from your local drive on any device as if it's a web page.

If you're testing the Save to Home Screen functionality of a Web App, 1 or 2 work, otherwise, option 3 is super easy once you're set up.

If you're just test the device dimensions, you can use the Device Emulator in your browser's Developer tools, as shown in the video below.