A coin that can only be mined on Samsung Galaxy, that would be "centralization" in my head ... then again, perhaps not worse than Bitcoin, which for almost all practical purposes are only mined on the AntMiner S9. Anyway, think of how disturbing that would be - tons of people always carrying lots of extra USB batteries with them, or never leaving home because they need to be tethered to the electricity network mining coins on their phones.

Also, the algorithm obviously has to be public - there is no way one can stop someone from making an ASIC - except by changing the PoW-algorithm by hardforks every second month or so.