I think we can set the validation of phones, emails in .yaml file under config. Can you please try the following
Copy {ROOT}\config\services\ui\ui.yaml at {ROOT}\extensions\defaultExt\config\services\ui\ui.yaml
Change the validation regex expression which is present at the end as shown below
validations:
regex:
phone: "^[0-9]{8}$"
Run command : php bin/console cache:clear from the root folder of suite8 instance.