The above posters are correct - Practice - Practice - and then practice more and become a confident shooter with which ever Gauge you choose.
It is the Payload one shoud e concerned with at the shot and while a 410 or even a 28Ga will kill pheasants you should use a gun that is suited for the game you are after. A 28 is too light in the majority of pheasant hunting situations IMO.
Most use a 12 - alot of people use a 20, and then some use a 16 . But which ever you choose practice.
Good luck
JW