Re: Naming each roku. Audio doesn't work with remote
You can name the devices at https://my.roku.com . Scroll down to "My linked devices" and click the pencil icon under Name. You can also use the Roku app.
Do your remotes have volume buttons on the side?
You can cast or mirror from your phone, but it's not something I've ever been interested in. However, there are plenty of people here that can help. What kind of phone do you have and are you trying to show your own videos or video from a website.
It's always helpful to include the model number(s) (not names) of your Roku devices that show under Settings->System->About when asking for help.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." If you appreciate my answer, maybe give me a Kudo.