Issue with setting MethodType when authenticator is phone_number

While trying to set SMS as the MFA, we are invoking IDX proceed() API with :- {authenticator: ‘phone_number’} and then {methodType: ‘sms’}.
This works fine and the transaction response have the authenticator method set properly in it. But, then if I need to change the method to voice, and invoke the IDX proceed API with :- {authenticator: ‘phone_number’} and then {methodType: ‘voice’}, it is not updating the methodType to ‘voice’. It still have the methodType as ‘sms’ itself.