It's OK to do—just realize a couple of things.
For the neutral serving two phases derived from a wye system, for 20-amp 120-volt loads on different phases, there will be a full 20 amps in the neutral—making it a current-carrying conductor...one of three.
Regardless of phase selection, if for whatever reason two grounded-circuit conductors are used in the same cable or raceway with two ungrounded conductors, you now have four current-carrying conductors.
