We have a function called strip_non_numeric_chars() which you can use in the Calculated Fields that will take care of this for you automatically.

The usage is very simple. For example, if you have a shipping address phone number like +1 555 209-4427 and you want to only export the numbers, you can use this formula:

strip_non_numeric_chars({{ shipping_address.phone }})

The above formula will return: 15552094427

There's an option to make an exception for certain characters as well. If you want to keep the "+" character for instance, you can slightly modify the formula to this instead:

strip_non_numeric_chars({{ shipping_address.phone }}, except_chars="+")

This will return just the numbers and the plus sign: +15552094427