I hit a short pop fly on the infield, the ball landed in fair territory and bounced foul; before it hit the ground in foul territory a infielder touched it. Is this a fair or foul ball?
If the ball has not yet passed the first or third base, then fair or foul is determined by where the ball is when first touched by a fielder (or where it comes to rest).
Your question seems to be asking if it bounded into foul territory, but hadn't yet touched the ground there, does that matter. It does not have to touch the ground to be foul.
From MLB Rules glossary (bolding mine):
A FAIR BALL is a batted ball that settles on fair ground between home and first base, or between home and third base, or that is on or over fair territory when bounding to the outfield past first or third base, or that touches first, second or third base, or that first falls on fair territory on or beyond first base or third base, or that, while on or over fair territory touches the person of an umpire or player, or that, while over fair territory, passes out of the playing field in flight.
If the ball was first touched by the fielder when in foul territory, it is not a fair ball. Doesn't matter if it has touched the ground in foul territory.
"You had me at landed in fair territory." - Rene Zellweger, probably
In case you think that's sarcasm, let me clarify. If it lands in-bounds, it's in play the same way that the batter is safe from being caught out. Just to check, we can think about what would happen if that wasn't the case. Then there would be no need to catch anything close to the line when you could just knock it out of bounds and give the pitcher another chance to throw a strike.