9to5Mac has put together a guide for remotely removing credit cards from your Apple Pay account just in case you find yourself in this very situation.
Jump on the nearest computer and log in with your Apple ID on iCloud.com
Go to the ‘Settings’ menu and click on your phone (which should have an Apple Pay symbol next to it)
In this menu, you should see your credit card information
A blue link that reads ‘Remove…’ will appear below the credit card number
Click it to deactivate the card from your Apple Pay account
Once you’ve recovered or replaced your phone, you can always add the credit card back to your account. Be sure to check out 9to5Mac’s guide in the source link below for a visual walkthrough of each step.