Owncloud is a wonderful solution to get rid of the big well-known cloud companies and to host contacs, calendar or files on an own server in your own country. But there is one downside: you have to take care for your data by yourself that nothing get lost.
If you delete unintentionally your data, for example during maintenance or updates of your server, it don't last long until your mobile phone is synchronized with the new vacuum. For that case I like to have backuped a vcf-File on a separate secure disk.
To create a backup of your contacts with owncloud call the following url in your browser and download the vcf-file to a secure place:
Substitue myowncloudurl.de with the url of your owncloud server. Depending whether you working on the server or in the local network you can use localhost or the ip-address. Further replace user with account-name of your owncloud account.