I would split up your validations. For checking if mandatory fields are filled I would do that in the custom save microflow. In that microflow check all the mandatory fields and give a response to the end user if some fields are left open.
You can then use the widget for those fields like phone numbers that need to be in a specific format. Allthough this also could be done in the custom save microflow with regex checks. Because I might be mistaken but with two phone number fields you will end up in the same situation. As soon as a validation check is done all the fields on the form will be validated.
So my advise would be to do all the validation in custum (sub) microflows before you save.