If you lose a phone or watch associated with Apple Pay, you need to sign in to your iCloud account via another device as soon as possible. When you mark your device as lost, you remotely lock it with a passcode, keeping your information secure. This also disables Apple Pay on the missing device. This is important so that no one will misuse your phone for payments via Apple Pay.
To find your device, sign in to https://www.iCloud.com/find. Or use the Find My app on another Apple device that you own.
You do not need to block your card in the P.F.C. app, as Apple Pay does not store your card details.