You can set up custom phone number masks in Global Settings > Custom Labels > Address > Phone > Format, where "A" represents an alphanumeric character and "9" denotes a number. To set up an international phone number format, such as +1-541-754-3010, you should enter A9-999-999-9999 into the phone format field. You can also use a sequence of A's to allow for a free flowing format to account for a wide variety of international phone numbers. Something like 999 999 9999 - 999 will allow you to add phone numbers with 10 digits and 3 digits for extension. Check CORE Help Center for details.
You can also create a separate label to be used in the additional fields of the address area if you want to keep auto formatting for US numbers and allow for international numbers as well. For that, rename the 'Home Phone' label to USA and the 'Mobile' label to 'International' and then enter the desired formatting for each label. Check out Custom Labels for details.