As far as I can tell just the Outboard BB is.
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According to the Phil Wood FAQ:
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.
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.