[Home](./index.md) > [@firebase/auth](./auth.md) > [PhoneMultiFactorGenerator](./auth.phonemultifactorgenerator.md) > [assertion](./auth.phonemultifactorgenerator.assertion.md) ## PhoneMultiFactorGenerator.assertion() method Provides a [PhoneMultiFactorAssertion](./auth.phonemultifactorassertion.md) to confirm ownership of the phone second factor. Signature: ```typescript static assertion(credential: PhoneAuthCredential): PhoneMultiFactorAssertion; ``` ## Parameters | Parameter | Type | Description | | --- | --- | --- | | credential | [PhoneAuthCredential](./auth.phoneauthcredential.md) | | Returns: [PhoneMultiFactorAssertion](./auth.phonemultifactorassertion.md) A [PhoneMultiFactorAssertion](./auth.phonemultifactorassertion.md) which can be used with [MultiFactorResolver.resolveSignIn()](./auth.multifactorresolver.resolvesignin.md)