Phoenix harass is great at all times of the game regardless of whether expected or not.
In terms of that comment, Ive found this not to be the case. Generally it depends on the match up for instance in both PvT and PvZ the turrets and spores come at a greate cost to the Protoss economy because you are bound to lose between 2-4 Pheonixs depending if your micro is actually semi decent. Which is a lot of cost investment considering the costs of pheonixes.
Also to actually make a decent harras with your pheonixes you do really need a reasonable amount of them because usually in thee early game their energy is quite low. For an efficient and viable harras probs 5-8 pheonixes otherwise it really isn't worth the effort.
To be honest the only really effective harrasment is in the versus Zerg and not at all times of the game mainly early to mid game.
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