There is no official NFC API from Apple, so there is no way to NFC directly from an iPhone app. However, there are some workarounds that might be possible, depending on what you're trying to do.
For example, if you're trying to read an NFC tag, you could use an external reader that plugs into the iPhone's headphone jack or Lightning port. The reader would then be able to read the NFC tag and communicate the information to your app.
If you're trying to write to an NFC tag, you could use a similar approach, but you would need an external writer that plugs into the iPhone. The writer would then be able to write the NFC tag.
Another option would be to use an NFC-enabled accessory, such as the
Sony SmartTags. These accessories can be written to and read by an NFC-enabled iPhone, and can then be used to trigger actions in your app.
Unfortunately, there is no way to do NFC directly from an iPhone app at this time.