Calculating Phase wise Energy in Three Phase System
In three phase three wire system, is it necessary to calculate phase
  wise energy?


With only three phases and no access to a star point on the load (if it is a star connected load and there's nothing to suggest that it is) then, it's impossible to calculate power or energy in any of the three parts of the load.

The only method to calculate load power is the two watt meter method and this doesn't distinguish individual phase powers: -



Picture from here.