Currently the situation is that all my (~600) contacts exist only on the phone, in a DAVx5 Address Book which is pointing at a (now non-existent since years) NextCloud instance. How to best get them into the new Radicale instance without them being deleted? There is nothing stored in the new Radicale setup, yet.
I’d recommend:Export the contacts with the Android contacts app to a .vcf. It generates vCards 2.1, so don’t import it directly to Radicale. However save it somewhere not on the phone as backup. Set up DAVx5 with the Radicale server. Sync; an empty address book should be created on the Android device. Import the vcf with the same Android contacts app, but to the new account. Verify that the contacts are now on the Radicale server. Delete the Nextcloud account.
The process is also shown here: https://www.davx5.com/faq/existing-contacts-are-not-synced
Does that help?