You won't have any issues, I have been using Calibre and uploading to Google Books for years. If there is DRM on the epub files, Google Books will alert you. In this case, just process/convert the epub in Calibre to an epub file. Calibre will remove any DRM.
You have to find a phone that is compatible with open source Linux Phone OS. Most of the OS websites give a listing of what phone make/model works. FYI, almost all the Google Pixel phones work.
Here are a few I am keeping an eye on when my Pixel 4a/5G stops getting updates from Google...this year. /
LineageOS/
GrapheneOS/
CalyxOS/
e.foundation/
Youtube videos and other websites are good sources on how to install, etc.
I think it both shocked and stunned the Garuda team when I showed it. They still can't open their eyes.