1...Nf6 is more flexible.
Why does Kramnik play 1.Nf6 instead of 1.c4

1. c4 e5 is fine for black. Also Kramnik used to play the Catalan a lot and by playing Nf3 first he probably can use some crazy move order magic that only GMs understand. Sometimes he transitions into Queens Gambit but I don't know the subtleties of this move order.
Maybe avoiding Albins Counter Gambit??? I know it's not that good but you still have to be prepared for it and this costs time.

In terms of move order when you play the English, it doesn't matter in so far as White after two moves is very, very likely ;-) to have a white pawn on c4 and and a white knight on f3. However, by playing 1.Nf3 first, you cut out whole complexes. Not only 1.c4 e5 as mentioned by Smositional, but also such variations as the Nimzo-English (1.c4 e6 2.Nc3 Bb4), because 1.Nf3 gives you the option of holding off c4 for several more moves (2.g3, 3.Bg2, 4.0-0, and perhaps even 5.d3), forcing Black to show his hand and allowing White to adjust his set-up accordingly.
Also, not all players respond the same way to 1.c4 and 1.Nf3, and I'm assuming (without a prior database check) that 1.Nf3 much more often leads to the Catalan than 1.c4 does. The Swedish GM Ulf Andersson nearly always opens with 1.Nf3, and regularly plays the Catalan, but isn't averse to transposing to the English.
When looking through Kramnik's games I've seen when he wants to play the English he will first play 1.Nf6 instead of 1.c4. Why does he do this? Does it avoid any variations of the English that are hard to play against?