We have also added the country select option which will be release soon check this
http://prntscr.com/117banq
After updating plugin you need to add this code to set default country selected
add_filter('wplms-phone_script_args',function($args){
$args['settings']['default_country_code'] = 'US';
return $args;
},10,1);
You can Also search and use your prefered country code from here
http://prntscr.com/117bct1