Looks like you've "Validation Rule" set to "Single Alphanumeric Word (letters, numbers, and underscores only)". That validation rule expects an alphanumeric word. You've supplied a number. I suggest setting "Validation Rule" to "Phone Number" or to "Custom REGEXP Validation" then use the following REGEXP based off the value you've supplied to the field.

/^\d*$/

I don't see how a recent CB update could have anything to do with this. That validation rules behavior is unchanged for multiple years now.