ISO/IEC 18092 and ISO/IEC 14443: what is the difference?
ISO/IEC 14443 describes a passive card being interrogated by a reader. ISO/IEC 18092, also called NFCIP-1, describes an interface where either device can drive the exchange. They share part of the physical layer, which is why the two numbers appear together and get used interchangeably.
Two standards, two ideas of who talks
14443 was written for cards. It assumes an asymmetry: one side has power and asks questions, the other is a passive object that answers. That model describes a badge at a door or a card at a terminal perfectly.
18092, published as NFCIP-1, was written for devices. It assumes both sides could be powered and either could initiate, which is what makes card emulation and the historical peer to peer mode conceptually possible.
Where they overlap
Both operate at 13.56 MHz, and the modulation and coding used at the lowest bit rate are shared. A tag can therefore be described accurately by either number depending on which aspect you are talking about, which is the whole source of the confusion.
Documentation and product sheets compound it by listing both without explaining that they are not alternatives.
Active and passive
The distinction 18092 adds is worth understanding because it explains a real behaviour.
In passive communication only one side generates a field, and the other answers by modulating it. That is what happens every time you read a tag. In active communication each side generates its own field in turn, which allows two powered devices to talk without one permanently powering the other.
Active mode is why two phones could in principle exchange data directly. Whether either mobile platform still exposes that usefully is a separate question, and the answer today is essentially no.
Whether you need to care
Buying tags: no. The tag type tells you what you need, and the ISO number underneath is trivia.
Reading a datasheet: mildly, because seeing both numbers listed is normal rather than a sign of confusion on the manufacturer side.
Writing software that talks to tags at a low level: yes, because the two standards define different frame structures and different command sets, and the platform APIs expose them separately.
For everyone else the useful summary is that 14443 describes the card world, 18092 describes the device world, and consumer NFC lives in the overlap.
Frequently asked questions
Which one does my phone use?
Both, depending on what it is doing. Reading a tag exercises the card model, emulating a card exercises the device model, and the hardware supports both because the physical layer is shared.
Is 18092 the same thing as NFC?
It is the core interface standard, but NFC as a product category also needs the NFC Forum layers on top: tag types, NDEF and activation. A device implementing only 18092 would not be interoperable in the way people expect from NFC.
Why do product listings mention both numbers?
Because both apply. The tag is compatible with the card interface and with the NFC device interface, and listing both is accurate rather than redundant, even if it is unhelpfully presented.
Does peer to peer mode still work between two phones?
Not as a supported way to share files on either mobile platform today. The mode exists in the standard, but the platform features that used it have been withdrawn or were never offered.