Instructions: Australian International format:
+61x xxxx-xxxx

The first x being the area code and the rest of the x's is the phone number.

The [2-9] is so we only require just one digit between two and nine inclusively.

The [:space:]] class ensures a space is used.

The last part, [0-9]{4}-[0-9]{4}$ tells the Regex engine that the number must have a group of four digits then a hyphen with another set of four digits ending with an end of string character.