REST API v2 Update Company phone_number / fax_number

Using the v2 REST API I cannot seem to update phone_number or fax_number if one does not already exist. Here’s a sample Get Company response:

{
  "id": "527314",
  "company_name": "Test",
  "phone_number": {
    "extension": "",
    "number": "(555) 555-5556",
    "type": "Work",
    "field": null
  },
  "fax_number": null
}

A sample Patch Request,
Uri: https://api.infusionsoft.com/crm/rest/v2/companies/527314?fields=fax_number%2Cphone_number
Body

{
  "phone_number": {
    "type": "Work",
    "number": "(555) 555-5550"
  },
  "fax_number": {
    "type": "Work",
    "number": "(555) 555-5551"
  }
}

Patch Response:

{
  "id": "527314",
  "company_name": "Test",
  "phone_number": {
    "extension": "",
    "number": "(555) 555-5550",
    "type": "Work",
    "field": null
  },
  "fax_number": null
}

This worked for me when I passed the field name for phone and fax.

{
  "phone_number": {
    "field": "PHONE1",
    "type": "Work",
    "number": "(555) 555-5550"
  },
  "fax_number": {
    "field": "FAX1",
    "type": "Work",
    "number": "(555) 555-5551"
  }
}

That’s really weird. I am getting exactly the same results using that patch body. The company’s phone or fax are still empty after that request. I tried using the other values for field as well, “FAX_NUMBER_FIELD_UNSPECIFIED”, “FAX1”, “FAX2”. They all left the Fax number as “null”. The patch does receive a success status code, it just doesn’t update the numbers.
I even tried creating a new Company with no phone/fax and adding to that, still no luck.

Edit: Additionally, if I add a number to the company through the web interface, the exact Patch request in my original post works to change the number, just not to add it if it’s not there.