There should be no need for customized phone number formats because phone
numbers already have standardized formats, which are recognized by Outlook.
And in those formats, phone numbers (and area codes) never begin with a "0" -
this despite the very common misconception that the leading "0" is actually
part of the phone number. In fact, it is not. The "0" is what is called a
"trunk prefix" or dialing prefix.

Australian phone numbers consist of an eight-digit local number and a
one-digit area code, with the area code "4" being reserved for mobile
numbers. The correct format is +61 (a) nnnnnnnn, and specifically for an
Australian mobile number, +61 (4) nnnnnnnn. That is the format to enter
numbers in Outlook Contacts, and yes, including the country code.