Well, the first three you mentioned are for providing power to other chips, the last 4 are RF amplifiers, they aren't really related. Why you need (or want) mu

Well, the first three you mentioned are for providing power to other chips, the last 4 are RF amplifiers, they aren't really related. Why you need (or want) multiple power management ICs: they are likely powering separate zones of the board which may have very different power requirements, e.g. need different voltages, need to be able to power up or down separately, or need particularly clean power. Why you need multiple RF amplifiers: Almost all phone today run on many different cellular frequencies and protocols, a quick look at the specs indicates the iPhone 6 supports: 800Mhz, 850Mhz, 900Mhz, 1700Mhz, 1800Mhz, 1900Mhz, 2000Mhz, and 2100Mhz along with various different signaling schemes. You can't handle all that in a single RF pathway.