you could use the predefined action "Transform & Copy Selection With Java Script" with this script:
async (clipboardContentString) => {
// remove whitespace and -
let phoneNumber = clipboardContentString.replace(/[\s-]/g, '');
// open whatsapp
let script = `/usr/bin/open whatsapp://send?phone=${phoneNumber}`
runShellScript({script: script});
return phoneNumber;
}
This would copy the number and immediately open whatsapp. If you want to copy separately use the predefined action "Transform Clipboard Contents" instead (the script stays the same)
