Hello @amaunsworth,
The main feature of this plugin is to get the country from the current customer automatically, you don’t need to set a default country because the plugin will get this info from the customer IP.
In any case, you can choose several preferred countries to display upper in the country list. To enable this, you have to add the preferredCountries
form tag this way:
<label> Your Phone:
[intl_tel customer-phone preferredCountries:us-ca-mx] </label>
In the example above your phone field will show United States, Canada and Mexico at the top of the list. You can so many codes as you need using two-letters country codes hyphen separated:

Please note if the user is using an ad blocker browser add-on, like AdBlock, the plugin will be unable to get the customer country.
Hope this can help you.
Best regards,
Yordan Soares