What is Power Mangement IC, How Does it supply power voltage to a Mobile Phones circuit

Power Management IC is a power IC, that manage,control and distribute and Supply Power voltages from the battery source to other corresponding circuits or chips.
It is highly designed to convert,regulate, stabilize current and voltages that flow across unto it.
A power supply IC Chips can divide and multiply certain voltage from one desired voltage source to any desired power output voltages.
Which is for example a battery voltage source  amounts at 3.7voltsDC while other components chips or circuit only requires the amount of 1.8volts, This 1.8volts  is the amount of voltage is what the power management IC are going to convert.
A block diagram below shows a brief details on how power supply IC converts and distribute certain desired
voltage from a battery power source to other corresponding circuits or components.

In a typical schematic diagram like in Nokia mobile phones, certain output supply power voltages were labeled as how much the amount of each output to supply power voltages to another circuits or components.
A failure of a power management IC to gain this following output voltage is also a failure to other corresponding components or circuits to work.

A picture below is an example layout of a power management IC mounted on a printed circuit board.

A deep familiarization of how this chips works including  its whole operation within a circuitry of mobile phones is  also a powerful tool in troubleshooting hardware problem issues on a mobile phones.