How to insert a character inbetween the string with different lentgh?

Hello.I need to insert a dash into a phone number after first

 

digit. I know how to do it using attribute manager and text editor only

 

if the length of the number is always the same. In this case is not. Is there a code I can put instead of "X" to indicate the rest of the value? If I will put fixed number the outcome is incorrect because of mentioned before different string length.

Maybe there is other way?

Thanks,

Cheers

@Left(@Value(phone_no),1)-@Substring(@Value(phone_no),2)