Problem is, every time you make a purchase from any online site the seller may end up with your name, address, phone number, email addy etc., all of which may be sold on and used for dodgy purposes. There is value to this information.
I use slightly different spellings of my first name on various sites, you can always plot which site the seller comes from (not that you can do anything about it, it's just interesting).
I do use one of those basic burner phones for all online sites (only because I'd go bonkers with all of the 'We've got your package', 'We're going to deliver your package', 'Your package is out for delivery', 'Your package will be delivered between 2.00pm - 4.00pm', 'Oops, we've had to change the delivery time' etc etc going to my iPhone).