Check repair terms and conditions for your country. These are for the USA:
Apple Inc. Repair Terms & Conditions
"5. Apple warrants for a period of ninety (90) days from the date of service (1) that service will be performed in a competent and workmanlike manner and (2) that all parts used to service your product will be free from defects in materials and workmanship, unless otherwise specified by Apple. Apple further warrants to the extent permitted by law, that batteries installed as part of Apple’s battery replacement service for Apple portable Mac computers will be free from defects in materials and workmanship for one (1) year from the date of service."
If your phone is replaced it will be with a refurbished unit as closely matching the old one as possible. Again, read the repair terms for your country.