iPhone 5 users who get a lot of mileage out of their speakerphone will want to visit Software Update: iOS 6.1.4 is here, and it's targeted right at you.
The small, 11.5MB update, applies only to Apple's latest smartphone, and includes, in Apple's words, an "updated audio profile for speakerphone." We'd presume that means that those on the other end of your speakerphone conversation might be able to hear you better, but it's not entirely obvious what the update does.
It appears that iOS 6.1.4 may also contain some of the latest security patches, though Apple had not updated details on the nature of those patches at the time this was written.
To update your iPhone 5 to the latest and greatest software, open Settings -> General -> Software Update and tap Download and Install when the update appears. You can also connect your phone to your computer and apply the update from iTunes, or download it manually from Apple's support site.