Is there an FM Receiver in an iPhone?

The short answer is NO, there is no FM receiver in an iPhone. You may have read that there is an FM radio chip in the iPhone. That much is partially true, because the chip that manages Wi-Fi and Bluetooth can also receive the FM band. But that doesn't make the iPhone an FM receiver, and it isn't why Apple chose that chip. They chose the Broadcom chip simply because it was the best around for Wi-Fi and Bluetooth. Need more? Here's an explanation:

To start with, it depends the definition of "FM receiver." I have an FM receiver (several, actually). In the real world an FM receiver has an RF component that can receiver FM signals, down converters that can produce audio output decoded from the FM signal, an antenna to receive FM signals, a connection to an audio reproduction source (e.g., speaker), and a means of tuning the FM band to select stations. Except for the RF component, the iPhone has none of those. It uses the multi-purpose RF microcircuit mentioned above that provides for Wi-Fi and Bluetooth. The chip can also can also decode signals in the FM band. But there is no way to get a signal into the chip to decode (an antenna), no way to tune the FM band (8 connections), and no way to get audio out (3 connections). The pins on the chip for this purpose are not connected to anything. So there is no way that any reasonable person can say that an iPhone has an FM receiver built in.

An FM antenna is a wire, ideally 30 inches (about 0.75 meters) long. The iPod Nano had an FM capability because you had to use it with headphones, and the headphone cable served as the antenna. You don't have to use an iPhone with headphones, and indeed, many people use it with Bluetooth headphones. So even if it had an FM capability, people using a Bluetooth headset or speaker connection Bluetooth couldn't use FM. Or anyone using the built in speaker.

Here is an experiment. Get an FM radio. Verify that it works. Now seal it into a metal box, so that no part of it is exposed outside the box. Now turn it on - oops, you can't reach the controls to turn it on, so that's out. Try again. Turn it on BEFORE you put it in the box, then seal the box. How are you going to change the station? How will you hear the sound? Of course, there won't be any sound, because there is no antenna outside the box. This describes a smartphone with a chip in it that can receive FM. It's there, but there are no connections to its FM functions.

But there is a really simple solution! For under $10 you can buy an FM radio. You can even buy a set of headphones with a built in FM radio that you can also use as the headphones for your iPhone. It will be extremely useful in emergency situations and cellular outages. It will work even after the battery in your phone has died, which will happen a few hours into an emergency.