The format of phone numbers for SDK is similar to that for Verify API. However the Verify SDK goes a step further in automatically validating your input in "To" field.
Therefore the number that you send your request to will be checked to ensure it is a valid number, and will be reformatted (from local/international phone number format, + symbol etc.). This means that you can send in any format and, as long as the number itself is valid, your Verify SDK request will go through.
For example the UK number 01234 567890 Nexmo SDK supports it being entered as: