For making international calls, use the full phone number including the country code.
Click To Dial
Click on the blue phone icon next to any phone field on any Salesforce record to start outgoing call.
Quick Find/Dial In Standby View
The Quick Find/Dial search field will try to locate the Contact/Lead or will function as a Phone input field.
To search for existing Contact/Lead, enter a few letters of the name of a Contact or Lead in the Quick Find field at the Standby View to start your search. Click on the blue phone icon next to the Contact/Lead name to dial.
To dial to a phone, type in the full phone number and click on the Dial button that will appear.