Using a phone number to infer country is possible (assuming, of course, the phone number includes a country code). If you choose to use this method, be aware that several countries share a country code. For example, Canada and the US both use country code +1. The United Kingdom, Jersey and the Isle of Mann share +44. An added problem occurs if you use Openprise to format phone numbers because you'll need a country to produce accurate formatting, so you can quickly run into a chicken and egg problem.
Using an email domain or website domain to infer country is straightforward. Just use the table Reference – Countries – Multilingual and the infer task template, matching your data's email or website attribute using "ends with" against the reference attribute Top Level Domain (TLD).