@woungchi3-
I applaud you wanting to spare your room mate from your TV noise but you may not be able to do it. For privacy concerns, most hotel and dorm systems are set up so that multiple devices connected to them cannot "see" or interact with each other. This prevents everyone using the same dorm system from accessing everyone else's accounts, but it could also prevent your phone from accessing your Roku.
Let me caveat that I have never done this myself so have no experience with it but ....
One thing you might be able to do is set up your own WiFi travel router and connect that to your dorm system. Then you connect your phone, your Roku, and any other devices to your own little private WiFi network.
Here are some at Amazon: https://www.amazon.com/s?k=travel+router+for+hotel+wifi
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