As an end user of powerschool, I am not your middleware.
If you, for whatever reason, feel you need dashes (-) between the area code, local prefix, and line number, great - that's on you, not the end user. I know how to read a phone number without dashes, I should not be required to enter an arbitrary separator for only your benefit.
Whilst I fully appreciate the necessity of input validation, you - the system owner/developer/administrator - are the responsible party for that input validation. Please enable/instruct your web development team to adopt any of the decades-old, widely used best current practices for input validation and data formatting in a way that does not excessively inconvenience the end user.