thank u i see it

wow! this is

OP had an off-by-one error in their for loop: loop counter i goes to 14 but the pattern variable has 14 characters, so the last iteration accesses phnum out-of-bounds

The C tests seem fine. Without more information, I'm going to close this issue.

This code is mostly correct. You are using a template string in your return value, and template strings will create exactly what you write in them... so your current return value includes extra quotation marks, extra spaces, and even linebreaks. So, for example, if the correct return value is (123) 456-7890, your function is returning the following (I'm using underscores to show spaces here, your return value does not contain underscores, they are spaces in your return value):

"(123)__
__456_-_
__7890_"

As a further note, you don't need to call the function yourself at the end of the code, the tests will do that for you. In this case, it doesn't matter that you call it yourself, though.