Zendesk support uses E.164 telephone number format to validate phone number entered if “Validate user phone numbers” is enabled in “Settings -> Customers”. However Salesforce does not provide such validation in telephone numbers.
A valid international E.164 phone number must include a country code, usually an area code, and a subscriber number. To avoid phone number validation error in Zendesk Support during record sync from Salesforce, the phone number entered in Salesforce need to follow the following format:
+ Country Code(Area Code)Phone Number
For example telephone number in USA it should be
This format should be applied to phone number from any country.