280 grams is a lot even for today's phones. 12 mm is half a inch. Very thick.
The other dimensions are 6.7 x 3.2 inches.
Ok, this might be a phone for people that want to prove a point but it's too cumbersome. How about starting with something reasonable and fit it with only what fits within those bounds? An example: 160 x 80 x 9 and 200 g. That would be a big phone but not bigger than many phones on sale.