my refurbished phone is faulty

Take it back to Apple. About your support coverage and service options - https://support.apple.com/en-us/HT202696

http://www.apple.com/legal/warranty/products/iphone-english.html

If I remember correctly, if this happened during the original warranty period the device is warrantied for the duration of the normal warranty period. If it happened later the warranty is for 90 days after the repair was performed if that is longer than the end of the normal warranty.

the 1 year would be for buying a referb outright from Apple. So Limnos is right, 90 days or after the repair unless that was longer than what you had on the warranty in this case since it was not a purchase.

https://www.apple.com/shop/refurbished/about

if it was refurbished by Apple and sold to you by Apple it should be warrantied for a year.

contact the apple store where you had it replaced.

Go back to that Genius Bar and explain your problem. That refurbished product (if Apple certified) is still covered by warranty.

Regards

Giulio

Yes, Limnos, your memory is okay :-)

Giulio