To preview the app(s) on a phone before publishing it, you can use the “Previewer App” module.
You can buy this module here: https://extensions.siberiancms.com/downloads/your-own-previewer-app/
Download the zip file and install it in your backoffice in Settings > Updates & Modules.
You will find how to create your previewer app in this documentation:
https://doc.siberiancms.com/knowledge-base/feature-application-previewer-setup-usage/