Your notes, photos, videos and voice memos are stored on your phone, not in your 1kr account. The account only holds your plan, phones and settings, so signing in on another phone doesn't bring your notes along.
Uninstalling 1krNote deletes its notes from the phone.
Moving to a new phone:
- Android: the phone's own backup (Google backup, or the transfer when setting up a new phone) includes the notes' text and settings, but not photos, videos or voice memos. Make sure backup is on in Settings → Google → Backup before switching.
- iPhone: an iCloud or computer backup of the iPhone, restored onto the new one, normally brings the app's data with it.
- Either way, you can share the notes you need before switching.
Signing in on the new phone may sign out the old one (see "All phones your plan covers are signed in").