A
You can get your phone to act as a hotspot and connect both Roku and computer to it (but bear in mind that this will count against your tethering quota, and not all plans include any tethering data at all). If you don't want to tether and you have unlimited mobile data, you can mirror the phone's screen to the Roku but you'll still need a router 'in the middle' to connect all devices to the same network; Roku doesn't support WiFi-Direct connections, so you still need a router to mirror content.