How to set which contacts account new contacts are saved to on the iPhone?

Manually

To ensure that newly created contacts on the iPhone are not saved, for example, to the sync.blue® CardDAV server but instead to an Exchange account that is also set up, you need to set the desired so-called default account for contacts on the iPhone (Settings - Apps - Contacts - Default Account).

Via MDM

For example, to set the existing address book of the personal Exchange account as the default account for contacts, it must first be set up on the iPhone. This way, the sync.blue® CardDAV account set up later will not become the default account, and new contacts will remain in the address book that was set up first. This is a limitation imposed by Apple iOS and cannot be influenced by sync.blue® or any type of MDM.

General tips for automated distribution via MDM 

Since Apple does not technically provide a direct MDM parameter to set the default contacts account, this behavior can only be controlled by the order in which accounts are provisioned. The following general recommendations have proven effective:

1. Ensure the order of profile installation data-id="12"Exchange (or the desired primary account) should always be added to the device first. CardDAV or third-party contact sources should only be distributed afterwards. This way, Exchange automatically remains the preferred default address book in iOS.2. Use the Enrollment Status Page (ESP)The ESP can help ensure that certain profiles or steps are completed before the user accesses the system. If Exchange is marked as "required," this ensures it is set up early and reliably. CardDAV can intentionally be excluded from the ESP and thus appear with a delay after enrollment.3. Use dynamic assignment / device groupsThrough dynamic device groups or filters (e.g., "device has Exchange profile"), you can ensure that CardDAV is only distributed once Exchange is actually installed. This prevents CardDAV from being added to the device "before Exchange" and avoids the order-of-installation issue.