It doesn’t really work that way, You would need to either find a web service / api that does the conversion or install the package into your n8n instance to use it in a function node or as a community node.
I did wonder if you could maybe do something clever with the webhook node but while I could happily create a small service that outputs the answer based on 2 inputs it didn’t work from an HTTP Request node.
You said that a web service / api that does the conversion can do the job but can’t work with small service with HTTP Request mode. Maybe use of API Service in this case has to have the correct environment to send and receive requests ??
using a phone number formatting library is definitely a good approach, especially if you’re working with international numbers and need consistent results