Lightning Web Components supports using components on desktop and mobile devices. On desktop, a variety of web browsers are supported. On mobile, supported environments include Salesforce distributed mobile apps. The differences between these two environments is more than just the screen size; there are new limitations, and also extended capabilities on mobile. To build components that perform well across mobile experiences, follow our guidelines for mobile-ready components.
Complete details are available in the Mobile and Offline Developer Guide, an essential companion to this guide when doing mobile development.