I did wonder why you used this expression and not “Contacts app”. It looks from your image above that your Posteo address book is the default. (In other words, the Contacts app probably appears as that address book, rather that a full list of your phone contacts). Thus although many phone contacts will be within Posteo, potentially many phone numbers will not show.
At the level Contacts app > Settings >
we see (line 2) Accounts, this is your image.
I think you need to watch carefully the changes as you apply changes to
- Contacts to display
But do you really want the Posteo account default – you can probably do this as long as
-
Contacts to display is All contacts.
-
Default account for new contacts is significant but of course does not affect what you have right now, except when you test adding a new contact.
- Of course there are other permutations depending on your needs.