Great news for all the comic fans out there: the Friendship is Magic #22 comic has been released today AND we did a huge update on our comic database, now featuring all Micro Series comics and Friendship is Magic #21 and #22.
FiM #22 has 7 covers, 6 of which are available right now, a 7th variant for Core Games will be released at BronyCAN. You can get the comic at your local comic store (might take a while), websites of various comic stores or online downloads/subscriptions through iTunes or Comixology.

Jetpack Comics and Larry's Comics have revealed the first Phantom Cariant for the Friendship is Magic comic series, which will be a cover for the #22 comic. Fans of The Incredible Hulk comics may recognize this cover: it's based on the original The Incredible Hulk #1 comic cover.
Phantom Variants are an initiative of various comic stores to deliver special covers, exclusively available to those stores. Or as Jetpack Comics describes it:

What is the Phantom Variant Project?  It's a cabal of retailers working together to produce limited edition exclusive comics for a select group of elite retailers!  It's the best minds in the industry working together to provide fun and exciting collectibles for fans and in quantities that help creators and publishers.  It is, quite simply, a limited edition variant that is shared between 20 or so stores.

It's unsure what this means for retailer exclusives covers, as various stores that participate in the Phantom Variant Project also (used to) release store exclusive covers.