Right now there seems to be huge gap between actually (close to)optimal use of phase cloak with currently defined phase mechanics and the way AI tries to use it.
First a simple question - how much does 1 second in phase cost? Obvious answer is - whatever is stated in ship stats as cloak upkeep. However, complete answer is - cloak upkeep + ship's flux vent rate.
Other important points:
-phase is entered instantly
-when you break phase, there is a short period while you are still immune & don't pay upkeep, but also do not vent flux. You also can fire. For further calculations i'll consider it to be 0.5 sec, though i don't know precise duration.
Consider following variant of shade: 125 phase in, 125 upkeep, 250 flux vent, 2500 flux capacity.
First second of long phase = 125(in) + 125(upkeep) + 250(regen loss) = 500
Not first = 125(upkeep) + 250(regen loss) = 375
Instant phase/unphase = 125(in) + 125*0(no upkeep) + 250*0.5(no regen while unphasing) = 250 for 0.5 sec immunity
This means that if ship is shot at less than once per 1.5 second it can dodge by instant phase/unphasing indefinitely (with perfect control though), more realistic estimate would be once per 2 seconds. Even human player can have good enough reaction to engage cloak right after he sees that enemy fired projectile weapon, so it's not impossible (beams are kind of special case, agreed).
Furthermore, while once per 1.5 seconds seems unrealistically rare for ship being attacked by multiple weapons, how the opponent uses these weapons is also important. AI will start firing right after unphase period. So time you get before you need to re-engage cloak = weapon fire up time (weapons like gauss cannon, but for most it's zero) + shot travel time (not quite zero even for beam weapons as it seems). With average speed projectiles at medium range this approach to phasing already starts to make sense, at long range it simply rules.
Conclusion: right now instant phase/unphase usually beats long usage of cloak both because it allows you to continue firing while phasing and stay immune longer (in terms of total *useful* immunity time). What is also important is the fact that it makes enemy waste flux, while simply staying phased lets them recharge it. Anyway - either precise mechanics behind phase needs an overhaul to make this sort of behavior inefficient or AI needs to build it's tactics around it.
PS1: tested it once more and found that unphase time can't be longer than time you spend phased. So if you have perfect reaction and can afford to phase for 0.1-0.2 sec, you can actually get even better efficiency.
PS2: Of course AI has even more obvious problems with phasing too, like staying phased under missile threat, which could easily be handled by available PD, or Doom inevitably killing itself through overload.
PS3: actually, i kind of remember where i've seen AI doing something close to described here - Paragon's Fortress shield handling. Hmm... I wonder if phase ships could be improved by letting them use variant of this logic instead (of course it needs to modified still, since *anything* is threat to them, while for Paragon it's only situations where incoming fire is too much for shield to handle normally).
Any comments on topic and the above wall of text?