I agree with the other commentors that we need an example in the post to make it easier to understand! Especially with all the different ways telephone numbers are handled country to country.
Luckily the linked Codewars page has an example!
createPhoneNumber([1, 2, 3, 4, 5, 6, 7, 8, 9, 0]) // => returns "(123) 456-7890"
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