There are several computer chips. Outgoing information is translated into digital. Incoming information is translated into analog. The microprocessor handles keypad and display duties, works with command and control signaling with the cellular base station, and coordinates other functions. The ROM and flash memory chips store information for the onboard operating system and databases such as phone directories.
Cell phones have tiny yet audible speakers and microphones.
Truly, cell phones are very much like telephones, radios, and computers all in one handy device. The large number of users keeps the cost per user low. Most cell phones today use monochrome displays, although full-color displays are available. Almost all phones have backlit panels.