Normalizing phone numbers with Contact Washing Machine and RegEx

We are trying to take phone numbers on our contact records and making sure they are only numbers (no dashes, no parentheses, etc.).

Trying to use the Contact Washing Machine app to do a find and replace on the phone number field, but struggling with the Regex to use in the find and replace entries in the configuration.

I'm a relative newbie on RegEx, and I've done some research, but not had much luck.

TIA