I asked PayPal why have a security phone code, they said below, did anybody know the extra security of a phone code is only as and when PayPal feel like using it, you have no choice.
“Most of the time you will be able to login or pay with PayPal by just entering your email address and your PayPal password as usual. But from time to time, we may ask you for a One-Time Passcode that PayPal will send you by SMS on the phone number you have registered in your profile.”
