Currently, the only practical use for Phoenix Down is Deep Dungeon (Palace of the Dead/Heaven-on-high) and adventuring forays like Eureka/Bozja. In regular content, players aren't going to be using Phoenix Downs when they can switch to a rezzing job in the overworld or just respawn in dungeons to prevent weakness. They have a use, but it's pretty niche.

I know rezzing is supposed to be the "thing" for healers/casters, but would it be such a travesty to balance to let everyone have access to Phoenix Downs as an in-combat rez option? It's just tedious nowadays to have to wipe (or sometimes struggle in vain) whenever the rez-capable mage(s) die in light party content like dungeons.

Not without some restrictions, of course:
  • Cast time increased to 10s.
  • any damage interrupts cast time (includes raidwides but not damage-over-time).
  • 5~10 minute cooldown between uses.

It puts pressure on players to carry a stock of Phoenix Downs with them at all times, but this could be alleviated by making them stackable as well as craftable and/or purchasable (either making for a passable gil sink).

This would make it difficult (but not impossible!) to use in-combat and prevents spamming from a single player. It's not going to save every run, especially trials/raids/prog where everyone was falling left and right in the first place. It will definitely help in dungeons where the healer dies to boss mechanics and is also the only rez option. Shouldn't have to punish the entire group when the healer is still learning mechanics and happens to die.

Raise is still the far superior option, but at least non-casters would have an option to try if the rez-capable mages go down.