There are 2 types of templates in Strato: Document Types and Templates under Client section. They use different data placeholders.
On the tab Client Documents, a new document can be added with a specific Document Type. The data in the specified placeholders will be automatically inserted. In case the data (e.g. Phone number) is changed later in Strato, the existing document will not be modified. To update the data in the document, the new document should be added to the Client Documents page.
Unlike Document Types, Templates can be used for specific actions like email notifications for one or several customers, so that their data can be automatically populated in each email. The instructions on how to create/modify Templates and Document Types are present in the Help documentation of Strato.