With default settings set by the wizard of Call2Teams you will not be able to call shortcodes from within Teams from a Flow control component (Fonzer dial plan), these will not be identified by the Dial plans set in Teams itself and converted to an international format so the code will no longer work.
You can add a new Dial Plan that caters for this.
In the Office365 environment, go to your Teams Admin module and then select Voice -> Dial plans
Create a new Dial Plan here using the "add" button and fill in the following details.
The completed regular expression shall be as follows: ^(\d{1,5}\*\d{1,3})$
(in this case, the calling plan can contain up to 5 digits and the short code up to 3)
If all is well, you can then enter the divert code in the field "Test dial plan" at the top of the Dial plan page and press the test button, if it shows that the number is an E.164 number you can assume that the short code will be correctly forwarded to the Fonzer platform.