I am a free user of the Duo Admin service, so I cannot set a policy to remove the call/text authentication feature. I have seen in the Duo forums that it may be possible for approved applications to add this option, so when I go to my Bitwarden application page in Duo I can disable the call/text option.
As many are aware, NIST has deemed that SMS 2FA is obsolete because of how easy it is to intercept an SMS/phone call or clone a SIM card.
While I can upgrade my Duo account (and pay a monthly fee) to allow this policy change, it would be nice to keep my free account if Bitwarden can make this change from their end.