M.R.
For my oldest I always warmed his bottle which caused a big pain and inconvience cause that's the only way he would take and if I was out i would always had to have warm it which was not always accessible. As far as for my youngest I learned not to start warming it from the beginning so I gave him powered formula w/room temp water which worked Great and if the bottle was cold from the fridge I would just let it sit 20 minutes prior to his schedule feeding and would be just fine or I would warm it just to take the chill off. At night "bedtime" I would warm it cause there is nothing better than a nice warm bottle of milk and I still do that which he likes and in the morning too. But he will drink straight from the fridge if neccessary.
I hope this helps.