For orders paid by PayPal, the buyer's information is collected on PayPal's checkout site, then PayPal reports those details back to us when they confirm completion of payment, with which we then process the buyer's order (issue links/codes, send emails, log the order details, etc.).
This data always includes the buyer's name and email, and can include a street address if you enable Require buyer's shipping address in the settings of each product that should trigger collection of an address. You can also require a phone number in your PayPal account settings under Profile (gear icon) > Account Settings > Website payments > Website preferences > Contact telephone number, though this may adversely affect your conversions for buyers wary of telemarketing.
For additional custom fields, you can set those up for each product requiring them by using our Variations/Variants feature:
