The Recipients count in the Review & Confirm window and the per-group counts next to each group name (e.g. "All users (243)") show how many unique numbers will be messaged. Sprwt super admins additionally have a Preview button on Compose that opens a Campaign Preview listing every recipient's User ID, Name and Phone after exclusions ("N recipient(s) found"). If you are not a super admin and need the list, ask Sprwt support or send a test to a small SMS list first.