I don't think any school in the T14 had one specifically for filipino.
There miiiight have been a couple that had Pacific Islander separately but since LSAC has deleted last years apps from LSDAS I can't check for you.
So I should probably check off "Other", then indicate Filipino-Guamanian? Because in truth that's closer to what I actually identify as than "Asian-American". (I'm sure a lot of Guamanians feel the same way as well)
Oh and thanks a whole bunch for your tips and advice. I've been asking around, but predictably not too many people are interested in talking about law school apps 
I would definitely try to differentiate yourself as a Pacfic-Islander, but not Guamanian. The box is asking for ethinicity, not nationality. The ethnicity of Guam is Chamoru, and even if you were born and raised there, you are not Chamoru. And, as I said, Guamanian would be a type of nationality, the way you are using it.
You have a wonderful diversity statement, but unless there's a pacific islander box, you have to choose Asian and explain that you're filipino. You can talk about your experiences in Guam, but I wouldn't recommend calling yourself Guamanian.