Update multi-factor-auth.md

[AlejandroGomezE]

Description
This PR aims to provide more clarity to the MFA phone sign in flow.

Related issues:
The current documentation shows an outdated function call for the mfa phone vericationId get funcion.

Description

Related issues

Release Summary

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • [] Android
  • iOS
  • Other (macOS, web)
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

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