The depth chart is in place for a reason.
That shouldn't change with the news from ESPN that Garrard will undergo arthroscopic knee surgery and that there's "no projection" for recovery (except to reflect Garrard's injury).
That is to say, Moore should be No. 1, and Tannehill should be No. 2. If and when Garrard is ready to play, they can reassess the situation.
If Tannehill was the backup, they would have reflected that on the depth chart.
If they didn't, they should have, because now they'll look reactionary if they suddenly throw Tannehill in as the team's starting quarterback.
Of course, we all know this is an organic situation. It is just a preseason depth chart after all.
What kind of message would it send to the team as a whole if the injury was the catalyst for a dramatic shake-up in the lineup?
That being said, as Philbin points out, this thing is far from over. Tannehill has begun to earn first-team reps in practice, and the coaching staff has made sure to point out that he's earned those snaps. Moore played some first-team snaps to open camp as well.
But up to this point, we've only seen then in practice settings. It's game time.
Who should start against the Buccaneers?
However, the Dolphins should do as they've done thus far in camp and continue to let the situation play itself out.