When you go on your phone you always have to turn on the RoonServer app (separate app from Roon) and it will run a fake server from the computer and if you go onto the app on your phone, choose different core at the bottom or cant discover core or something like that. Then you'll notice that two server addresses show up on the display and try each one out. One of them is for the real Roon which would be for paying members and will send you to the login screen. The other server will be the one that bypasses the login page and directly connects you to your computer. Once you click on that, your all set and you don't have to do "select the server" again because the Roon app on your phone now thinks the fake server is your real core.
If anyone has any questions about how to install on macOS or iPhone (iOS) / Android, let me know I'll be happy to help because I successfully did this. I might be slow because I only check this forum once a week and I'm sorry but if you write a question I'll try to get back to you as soon as possible.