I thought the RFID is at 13.56M, right? Which is much different from UHF.
I remembered my colleagues, when designed a RFID for a mobile phone, just maintained the antenna area is above 1200mm^2, and at test, just measured the inductance is about uH, then it's OK for phone. Hope I am right in these data.
The NFC in phone is just a function, not like a reader, which has much more requirements.
About the circuit, you can search some phone NFC circuits as refer.