The PHL files are actually known as Amazon Kindle Popular Highlights File; used to store the Popular Highlights of an eBook associated with Amazon Kindle e-reading device. The Popular Highlights is one of the smart features offered by the Amazon Kindle, which can be observed while reading an Amazon Kindle eBook on a Kindle eReading device. These are usually marked with a gray dashed underline. The PHL file contains the Popular Highlights related information; stored in XML form. The information could be the starting and ending positions of annotation as well as the number of users that have highlighted the passage.
Details of Kindle Popular Highlights
By using the Amazon Kindle eReading device, the readers can highlight passages, sections, or phrases. When the highlights sync with the Amazon Kindle account they get shared with Amazon. Amazon aggregates those highlights into Popular Highlights. The Popular Highlights display the most highlighted passages or sections that readers have added to the remotely available Kindle e-books. These appear as underlined text in a Kindle book when more than ten people have highlighted that same passage or section. It sounds like a nice feature theory, but in practice, it may look weird to some people. The Popular Highlights appear in many Kindle eBooks. A reader will come across underlined text while reading, along with a little annotation saying that there are “120 Highlighters” or however many there are.