AzureB2C Custom Policy - 2 Factor Authentication, mobile number not shown

Question

im stuck for days in an AzureAD custom policy for 2-Factor Authentication login. I design a log in user journey where after "e-mail address and password" in the next orchestration step the users (stored) phone number shall be displayed such that an SMS via a 3rd party provider I want to integrate is sent. After username and password are correctly evaluated I also get forwarded to my 2-factor-authentication page. But there I don't get my mobile phone number displayed. I know it is there, when I have AppInsights running I see it in the logs, but don't know how to grab it:

I use the technical profile "AAD-UserReadUsingObjectId" to get the mobile or strongAuthenticationPhoneNumber variable.

       <TechnicalProfile Id="AAD-UserReadUsingObjectId">
        <Metadata>
        <Item Key="Operation">Read</Item>
        <Item Key="RaiseErrorIfClaimsPrincipalDoesNotExist">true</Item>
        </Metadata>
        <IncludeInSso>false</IncludeInSso>
        <InputClaims>
        <InputClaim ClaimTypeReferenceId="objectId" Required="true" />
        </InputClaims>
        <OutputClaims>

        <!-- Optional claims -->
        <OutputClaim ClaimTypeReferenceId="signInNames.emailAddress" />
        <OutputClaim ClaimTypeReferenceId="displayName" />
        <OutputClaim ClaimTypeReferenceId="otherMails" />
        <OutputClaim ClaimTypeReferenceId="givenName" />
        <OutputClaim ClaimTypeReferenceId="surname" />
        <!-- <OutputClaim ClaimTypeReferenceId="mobile" /> -->
        <OutputClaim ClaimTypeReferenceId="strongAuthenticationPhoneNumber" /> 
      </OutputClaims>
      <IncludeTechnicalProfile ReferenceId="AAD-Common" />
    </TechnicalProfile>`

and in the next orchestration step i want to display it by using a technical profile Custom-SMS`

      <TechnicalProfile Id="Custom-SMS-Verify">
      <DisplayName>Custom-SMS-Verify</DisplayName>
      <Protocol Name="Proprietary" 
      Handler="Web.TPEngine.Providers.SelfAssertedAttributeProvider, Web.TPEngine, 
      Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
      <Metadata>
        <Item Key="IpAddressClaimReferenceId">IpAddress</Item>
        <Item Key="ContentDefinitionReferenceId">api.selfasserted</Item>
        <Item Key="language.button_continue">Continue</Item>
        <Item Key="UserMessageIfClaimsTransformationStringsAreNotEqual">Incorrect 
       verification code. Try again.</Item>
      </Metadata>
      <CryptographicKeys>
        <Key Id="issuer_secret" StorageReferenceId="B2C_1A_TokenSigningKeyContainer" />
      </CryptographicKeys>

      <InputClaims>
      <InputClaim ClaimTypeReferenceId="strongAuthenticationPhoneNumber"  
         AlwaysUseDefaultValue="true" />   <!--AlwaysUseDefaultValue="true" -->
        </InputClaims>

      <DisplayClaims>
       <DisplayClaim ClaimTypeReferenceId="strongAuthenticationPhoneNumber" Required="true" 
        />
  
        <DisplayClaim DisplayControlReferenceId="phoneVerificationControl-readOnly"  />
        <DisplayClaim DisplayControlReferenceId="phoneVerificationControl" />
      </DisplayClaims>
      <OutputClaims>
        <OutputClaim ClaimTypeReferenceId="phoneNumberString" Required="true" />

         <OutputClaim ClaimTypeReferenceId="strongAuthenticationPhoneNumber" Required="true" 
        />
        <OutputClaim ClaimTypeReferenceId="newPhoneNumberEntered" DefaultValue="true" />
        </OutputClaims>
        <UseTechnicalProfileForSessionManagement ReferenceId="SM-MFA" />
       </TechnicalProfile>

        </TechnicalProfiles>

The username+pw login works, it also directs me to the next page for the two-factor-Authentication but I always just get and empty field type in a telephone number or get some default-value I set displayed but I can't get the variable "mobile" or "strongAuthenticationPhoneNumber" shown. Anyone who solved this, it sounds like a pretty standard. This is where I got the the custom-sms-verify technical profile from: https://github.com/azure-ad-b2c/samples/blob/master/policies/twilio-mfa-psd2/policy/StepUpPSD2/TrustFrameworkExtensionsPSD2StepUp.xml

And this is how currently the three Display Claims in "Custom-sms-verify" look like...no filled in mobile phone number anywhere, just textboxes.

(I use a custom div='api' but this of course just changes how it looks like compared to e.g. AzureBlue design)

Best regards, Lukas