Apologies in advance, no insult intended. sometimes its the little things that catch us out.
Can you confirm:
- Phone cover off
- NFC turned on
- Screen on and unlock
- You are running TagInfo by NXP (or similar)?
- You have tested also with a full size HF card.
- or with Diagnostic card.
- Have you also checked the phone wiki that may have tips and tricks for your phone model?
All this just to get a clear starting point