Give him a few days to get the idea that you are the one he needs to look to for the milk. The nipple on the bottle does not feel like mom, and you holding it is not the same as butting up against a nice warm softer udder... and it just doesn't taste the same... but in a few days he will "get it".
How old is he?
Try standing next to him if possible, so he has to bend his neck a bit to the side and don't hold it too high so he doesn't get it into his lungs... think about how "high" the cow's teats were... for him to reach... a little more of a pita to do, but he will not suck air and will not get it down his lungs that way...
And if she didn't have big teats,,, you might want to try the sheep/lamb sized nipple...they make them to go on a 2 qt bottle... that is all I use on my calves... it is closer in size to most all the cows teats unless it is a big old uddered cow with fat teats... I know it takes a few more minutes... but they seem to "get it" better when the "teat" is not so awful big....