Updating mobileNumber using graph giving { }

I would like to add phone number to existing Azure AD users. I don't want them to manually enter their phone numbers to get code for MFA.

I am trying to do this from graph like this:

PATCH https://graph.microsoft.com/v1.0/users/id

{
  "mobileNumber" : "############"
}

This gave me No content - 204 status with empty brackets { }

Now I can see phone number added on user profile but it is still asking users to enter phone number to get code.

How can automate this process? Any ideas

PS: I have administrator role on my tenant so I hope I'm not missing any permissions.

Please note that, you need to create phone authentication method instead of updating mobileNumber property in user's profile.

I tried to reproduce the same in my environment and got below results:

To create phone authentication method, I used below graph query:

POST https://graph.microsoft.com/v1.0/users/<userID>/authentication/phoneMethods

{
"phoneNumber": "+91 9xxxxx4004",
"phoneType": "mobile"
}

Response:

When I checked in Azure Portal, phone number added successfully in user's Authentication methods like below:

Go to Azure Portal -> Azure Active Directory -> Users -> Your user -> Authentication methods

When user tried to sign in, it automatically displayed added phone number like below:

When user selected that option, they will receive code to their phone number which they need to enter here: