Why do we use coke instead of coal in order to reduce FeO as basic reaction in ironmaking process?
The single most important factor is strength ( mechanical compressive ); coal is heated to make coke, the resulting coke is stronger than the original coal. Also, coke helps to make the charge of iron oxides and limestone more porous to permit gas flow up and droplets of liquid iron and slag down. The coke oven heating drives off volatiles from the coal, which are a valuable source of chemicals, and contain much of the undesirable $\ce{S}$ and $\ce{P}$, which would otherwise go into the pig iron. Minerals like silica (ash) remain in the coke but they are easily collected by the slag. A bit off topic, but powdered coke and gasses are blown into the bottom of the blast furnace to provide more $\ce{C}$, which makes modern blast furnaces much more productive than 60+ years ago.