Is the update in this MERGE Statement redundant?

I'm trying improve the performance of a complicated stored procedure. Inside the stored procedure is the following MERGE statement. I'm not very familiar with the MERGE syntax.

The [Contact].[PhoneNumber] table looks like this:

CREATE TABLE [Contact].[PhoneNumber](    [Id] [int] IDENTITY(1,1) NOT NULL PRIMARY KEY,    [PhoneNumber] [nvarchar](255) NOT NULL    [InsertedAtDateTimeUTC] [datetime2](7) NOT NULL DEFAULT(sysutcdatetime()))

The merge looks like this:

;WITH _ContactPhoneNumbers ([PhoneNumber]) AS (    SELECT DISTINCT ([#ChannelData].[CallerAni])    FROM [#ChannelData])MERGE [Contact].[PhoneNumber] WITH (HOLDLOCK) _targetUSING [_ContactPhoneNumbers] _source ON [_target].[PhoneNumber] = [_source].[PhoneNumber]WHEN NOT MATCHED THEN    INSERT ([PhoneNumber])    VALUES ([PhoneNumber])WHEN MATCHED THEN    UPDATE         SET [_target].[PhoneNumber] = [_source].[PhoneNumber]        OUTPUT INSERTED.[Id], [_source].[PhoneNumber] INTO #Contact_PhoneNumber_Output ([Id], [PhoneNumber]);   

I read this as:

If the PhoneNumber does not exist in the [Contact].[PhoneNumber] table the merge inserts a new row into the [Contact].[PhoneNumber] and returns the new Id. If PhoneNumber does exist then the merge updates the PhoneNumber to be the same value, and returns the Id for the existing row.

Is the UPDATE redundant?

If it's redundant I'll take it out and see if it increases the performance. There are several MERGE statements in the stored procedure which follows the same pattern (with the UPDATE) so it could be a useful gain.

The Id is returned even if it exists, as it's used as an FK in a further insert.