Yes, it works with both enabled as SMS verification plugin factors in multiple phone fields ie. s_phone_mobile, s_phone_land, custom etc.
I think that 'Add phone to register page' option is intended for older themes that don't have mobile fields so if you enable it on a newer theme you'd be duplicating as it uses the same id s_phone_mobile.
Just make sure not to enable language in url (beta feature introduced in 8.1.1) as there's a bug that breaks the SMS Verif/Business Profile plugins which @MB is hopefully working on.