What Boom mic is compatible with a smartphone?
Most mics that are designed for DSLRs (such as many of those made by Rode) should be able to work with a smart phone as well (through the use of some adapters).  They just work on a standard line input like you have for a PC and through a splitter cable, most cellphones support the same kind of line input as a PC or DSLR has.  

It is actually even possible to plug a full blown ASIO audio interface in to many android handsets and do recording from phantom powered XLR booms, but that probably defeats the point of using your phone for recording.