Solution 1: via Apple iCloud
Use the "Apple iCloud" application to synchronize contacts with the iPhone. The prerequisite is that iCloud contacts have been activated on the iPhone.
Solution 2: via CardDAV
On the iPhone:
- Open Settings -> Contacts -> Accounts -> Add Account
- Server: directory.sync.blue
- Username: API_KEY (replace with your own API Key, which is displayed when setting up a sync.blue® connection)
- Password: API_KEY (as in Username)
- Description: sync.blue
- Advanced Settings
- Use SSL: yes
- Port: 443
- Account URL: https://directory.sync.blue/API_KEY
Solution 3: via Microsoft 365 / Windows Live
After adding the account, the contacts are natively synchronized with the smartphone including subfolders.