phone field on checkout page is not required anymore

Hey,
we are using woocommerce version 3.0.4. Since we updated to 3.0 the billing phone field on the checkout page is not required. I already checked in woocommerce/templates/class-wc-countries.php but in line 1115 “billing_phone” required is set to “true”. Is there another file were this is set? or is there a filter blocking it?

Thanks for your help!