Taylor Swift and Brittany Mahomes Exchange Numbers, Friendship Not for Show

The budding friendship between Taylor Swift and Brittany Mahomes isn't just for cameras on Sundays ... they've exchanged phone numbers and they're giving BFF vibes!!!

Sources close to Taylor and Brittany tell TMZ ... they swapped digits the first time Taylor went to a Kansas City Chiefs game to cheer on Travis Kelce, back on Sept. 24, and they've kept in touch ever since -- texting each other even when it's not gameday.

We're told Taylor and Brittany don't only see each other at Chiefs games ... and all their fun times NFL fans see on camera aren't just for show, as some folks are speculating.

Case in point ... Taylor and Brittany took shots together at Travis' after-party for the first game TS attended, as the WAGs were hanging out at the shindig.

From there, they progressed to hugs and dances in the players' family stadium suites ... and then this past Sunday, Taylor and Brittany debuted their new handshake to much fanfare.

Travis and quarterback Patrick Mahomes have a strong connection on and off the field ... and the same can be said for Taylor and Brittany.