I believe PHX is a seasonal Mint destination for the winter. In the summer it will be all-Y.
According to their
announcement from May:
This winter, every flight heading to Phoenix Sky Harbor International Airport (PHX) will feature Mint, offering nonstop comfort and excellent cuisine from JetBlue's East Coast focus cities - New York, Boston, and Fort Lauderdale.
JetBlue is not only adding Mint but doubling service from New York and Boston to Phoenix and reintroducing service from Fort Lauderdale to Phoenix
JFK-PHX will be 2x daily with Mint for the winter.
-J.