No, Roku channels cannot be streamed to another device via an app. They are designed to strictly play to a video display via HDMI, or a few models with analog connections. The Roku apps that are available allow controlling the Roku, and in some cases streaming media from the phone/tablet onto the Roku for display.
Dan
Roku Stick (3600), Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.