Contacts from iOS/webdav missing number

Nextcloud version (eg, 20.0.5): 27.1.1
Operating system and version (eg, Ubuntu 20.04): openSUSE Leap 15.5
Apache or nginx version (eg, Apache 2.4.25): Apache
PHP version (eg, 7.4): replace me
iOS version: 17.0.3

The issue you are facing:

On iOS I have my nextcloud contacts connected via webdav. I am added to a iMessage group chat and I want to add some of the contacts to my address book. Doing so leads to an entry in my Nextcloud addressbook. However, the phone number is missing. It is there on my phone and literally the only other information other than the first name.

Is this the first time you’ve seen this error? (Y/N):Y

Steps to replicate it:

  1. On iOS press on some kind of currently unsaved contact instance, e.g. in a group chat.
  2. Choose “Create New Contact”
  3. Save
  4. Open that contact on Nextcloud Contacts
  5. No phone number is saved

Edit: If I edit the little label for the phone number in the iOS Contacts app from the default phone to e.g. mobile, it will make the change and Nextcloud will show the number.

It seems that the webdav server does not accept or cannot read the default phone label that iOS assigns to new contact numbers?