When you have created a page template that you wish to share with the organization you can do it through two different paths:
Share template when you are creating it
Share template later on from the template settings
Share template when you are creating it
When you are creating a workspace you can configure that the workspace is visible to the organization right away.
Navigate to a page that you wish to create a template from
Click on "Page menu (The three dots "..." next to Edit page button)
Click "Duplicate page"
Select "Create a new page template"
Name your new Template
Click "Duplicate"
Click "Template settings" on the yellow top bar
Select "Organization" under Template visibility inside the organization
Click "Save"
Share template later on from the template settings
If you have already created a template from a page and wish to share with your organization later on. You can do it easily by following these steps:
Navigate to Templates > Page templates
Make sure that you are on "My Templates" tab
Find the Template you wish to share
Click on "..." next to the template name
Click "Edit template"
You will be taken to the template workspace
Click "Template settings" on the yellow top bar
Select "Organization" under Template visibility inside the organization
Click "Save"
Now the workspace template can be found in Organization templates for all the admins in the organization.