Hello Basil,
If you want to output a custom field value from a settings page, please add the attribute object_id
which is the option name, and attribute object_type="setting"
to the shortcode.
For example:
[rwmb_meta id="phone" object_id="site_option" object_type="setting"]
Please follow the documentation
https://docs.metabox.io/shortcode/
https://docs.metabox.io/extensions/mb-settings-page/#using-code