How to insert regex into json?

Question

JSON

I have a regular expression like this: /\(?([0-9]{3})\)?([ .-]?)([0-9]{3})\2([0-9]{ 4})/
but in general it can be anything,
I need to send it in json format,
I went to this site: https://www.freeformatter.com/json-escape.html#ad-...
and formatted regex there to json and got this: \/\\(?([0-9]{3})\\)?([ .-]?)([0-9]{3})\\2([0- 9]{4})\/
it is passed but doesn't work because it has two characters in a row \\
is it possible to pass regex to json normally somehow?