Hi Sonny,
At present, the functionality is limited and doesn't allow you to define your own regular expressions for showcasing phone number in a specific format.
Currently, the phone number format is defined by data policy named phone described in schema xtk:common.
If you wish to bypass the default setup, you can do the following
extend the nms:recipient schema, and create the attribute <attribute desc="xxx" name="mobilePhone" type="string" label="yyy" length="32" dataPolicy="none"/>
We are removing the default data policy associated with this attribute. Then you can save the phone number as you want as it is a string field.
You can also define a computed string on this attribute which can show the mobile number as you want it.
Hope this helps.
Regards,
Vipul