"Wrong phone format" but no explanation of why

[Coehill]

When adding a telephone number to a building, it often displays a warning "Wrong phone format" but it does not specify what it should look like.

In my opinion, it would be useful to either add a tooltip/explanation in the error message. Or, automatically format the phone number when tapping enter if possible. Ideally, force it so the number is formatted as you're typing. This should also work when lasting phone numbers.