I have try a set of regular expression on online tools.
The result perfect match with my input.
However, when I copy and paste the same things into RegexValidator, it shows me ERROR in Invalid ICU message. Missing '}' ^(+\d{3}\s)?(?\d{2,3})?\d{3,4}[\s]\d{4}?$
Try escaping all \ symbols with \\ - the Pattern property is a string. In addition you may need to create a page property and assign the pattern to it. Then set the Pattern property of the component to said page property.