Rank these skills from 1 to 5, five being best.

Special Spiral: 4-5
Great for:
Either Phase (Depending on build)
Reinforcement Maps (GHBs, LHB, etc.)
Tempest Trials

Swap: 3-4
Great for:
Enemy Phase
(Okay with everything else)

Guard: 4
Great for:
Either Phase (Depending on build)
Arena (Not specifically for points)

Obstruct: 1-3
Great for:
Enemy Phase

My thoughts, probably did this wrong, though.

Depends so much on the unit. Special spiral is 5/5 on Lilina player phase but maybe 2/5 on Sheena, especially for player phase but to some extent even on enemy phase because the ignis probably doesn't hit hard enough if she's not using Wo Gun, and maybe even then not hard enough.

Swap is at least 4/5 on armours if you don't want traffic jam but more like 2/5 on fliers because you can't use it to run away.

Obstruct is maybe 3/5 at best on something like wary fighter L.Hector in GHB, and generally 1/5 on anything in arena.

Guard is 4/5 or 5/5 on some units for arena, 2/5 or 1/5 on others, and generally 2/5 on most units in any mode that doesn't feature player-built opponents.