Genesys Cloud - Main

You could use the external contacts feature. There are 4 phone number fields you can populate and you could potentially use the "Other" field as a fax number. I will note the need for a fax phone number for our backlog. https://help.mypurecloud.com/articles/about-external-contacts/

There are a few different ways to add contacts - manual, via a csv, syncing with Salesforce and other customer repositories. Here's an article that walks you through the variety of options. https://help.mypurecloud.com/articles/about-creating-repository-of-customer-data/