Adding a credit card on 2 different iPhones for Apple Pay

Yse, you absolutely can. You can add the same card to multiple devices, however depending on bank's risk management rules, if name on tha card doesn't match name on iTunes account, there might be a need for additional authentication ( like s call to customer care). Apple Pay supports up to 99 tokens on the same account and no differentiation whether the token used on the same devbice multiple times or on multiple devices.

natapech is absolutely correct. My wife and I have separate Apple IDs and adding our Visa issued by Bank of America on each of our iPhone 6s worked just fine. We are both successful users of iPay.

Untrue. If you are just here to get "points" then please remove yourself. Uneducated responses that are not factual are pointless and annoying. Check Amex website - Can I put my Card on multiple devices?

Yes, you can add your Card on up to 10 devices. Please note that your Card must be added to each device separately.

https://www.americanexpress.com/us/content/apple-pay/faqs.html

No. Only on your device.