Cloud.typography is designed to deliver fonts to web browsers, including mobile ones. If you’re building a web app that runs in a browser, just add its domain to your project using the domains panel.
If you’re building an app that will run native on the device (for example, an iOS app distributed through the App Store), you’ll need to embed the font files directly into the application itself, which requires a different kind of font license. For more information, see Using Fonts in Apps with App.typography.