We recommend to use the E.164 formatting. This is an internationally-recognized standard phone number format that will help to ensure deliverability of calls and sms messages across the globe.
In general that means: ['+' country code][national phone number without leading 0][telephone number]. Overall you do not use any spaces, hyphens or parentheses. A well formatted UK phone number looks like: +447911123456.
More international formatting info? Check out our more in-depth guide about how to format international phone numbers. Or have a look at the following [this wiki](https://en.wikipedia.org/wiki/List_of_country_calling_codes#Alphabetical_listing_by_country_or_region .).