Which Phil Wood bottom brackets are compatible with Shimano XT cranks?

Question

As far as I can tell just the Outboard BB is.

Answer 1

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.

Answer 2

Shimano uses a JIS taper (Japanese Industrial Standard). Take another look at their catalog and any bottom bracket (there are too many to list) that uses the JIS standard will work with your XT cranks. DO NOT get the JIS low profile, as those will not fit, stick with plain JIS and you should be GTG.