Hi Julie,
Before you embedded your metadata, did you make sure it was a QIIME-style tab-delimited mapping file, with a header line that looks something like this:
#SampleID BarcodeSequence LinkerPrimerSequence CollectionDate Material phinchID Description
You need the #SampleID column for Phinch to pull in the sample names.
If this all looks OK, would you mind sending me your .biom file? I can look through it and get a better idea of what's wrong. My email is holly dot bik at gmail dot com.