Active and passive communication explained
In passive communication only one device generates a field, and the other answers by modulating it. In active communication each side generates its own field in turn. Every exchange between a phone and a tag is passive, which is precisely why the tag needs no battery.
Two ways to hold a conversation
The distinction is about who generates the field, and it is separate from the question of which operating mode is running.
In passive communication, one device produces a field and keeps it up throughout. The other lives inside that field and answers by varying how much energy it draws. In active communication, each device produces its own field when it is its turn to speak, and drops it when listening.
Passive, which is what you use
Every read of a tag is passive communication, and it has to be, because the tag has nothing to generate a field with.
The same is true when your phone acts as a card at a terminal. The terminal supplies the field, the phone answers within it. The phone is powered, of course, but it is not producing the field for that exchange.
So both of the modes anyone uses daily run passively. The consequences follow directly: one side supplies all the energy, the exchange stops the instant the two separate, and only one side may speak at a time.
Active, and where it went
Active communication requires both sides to be powered, which excludes tags entirely. Its purpose was to let two capable devices talk without one permanently powering the other, and it was the basis of peer to peer mode.
Since peer to peer disappeared from the platforms, active communication has almost no presence in what an ordinary user or developer encounters. It remains in the specifications published by the NFC Forum and is largely absent from practice.
A confusion worth clearing up
Passive communication and a passive tag are related but not the same thing, and mixing them causes real misunderstandings.
A passive tag is an object with no power source. Passive communication is a way of running an exchange. A powered phone emulating a card is participating in passive communication while being anything but a passive device.
The practical version: ask who is producing the field. That question answers whether the exchange is passive, and it also tells you which side will run out of patience first when the two are separated.
Frequently asked questions
Is my phone active or passive when reading a tag?
It is producing the field, so it is the active participant in a passive exchange. The tag is the passive side. The mode as a whole is passive communication because only one field exists.
Do two phones use active communication?
They would have, through peer to peer mode. Since that mode is no longer available on either platform, two phones exchanging data over NFC is not something you will encounter.
Does active communication reach further?
Not meaningfully. Range is governed by antenna geometry and field strength rather than by which side generates the field, and both devices are still subject to the same near field limits.
Why does the exchange stop when I move the phone?
Because in passive communication the field is the power supply for one side. Remove the field and that side stops existing electrically, mid sentence if necessary.