Which Phil Wood bottom brackets are compatible with Shimano XT cranks?
According to the Phil Wood FAQ:


  What is the difference between JIS, JIS low profile, and ISO
  tapers?
   Phil Wood offers all three tapers to try and best meet the needs of our
  customers who are using square-tapered
  bottom brackets. An explaination of
  the different bottom bracket tapers
  can be found here. In brief, most
  modern cranks will take the JIS
  (Japanese Industrial Standard) taper,
  in addition to Campagnolo cranks
  produced before 1994. After 1994,
  Campagnolo moved to the ISO (a.k.a.
  Campy) taper. The less common of the
  three tapers offered is the JIS low
  profile, which is used in some
  specific older-model Dura Ace cranks.


Since Shimano square-taper cranks are J.I.S. (not low-profile), this means that all Phil Wood bottom brackets with JIS spindles are compatible, as well as Outboard Bottom Brackets.