Scout

You have 2 Stargates so you can pump out pheonixes fast. Thats why i put in here if your a better player than me you mite want to squeeze a couple sentries in early than i do so you can get a pheonixes scout around 8-9 min and if you see spire abort and chrono pheonixes, throw down A templars archive and go into storm, then archons when you take your third.

Although most like you said most zergs unless your lower levels don't go fast mutas, and instead if they see anything stargate they go immediatly into hydras which is bad because you will have enough voids to crush their hydras in low numbers. Furthermore, zealots with voids are really nice because, alot better than Sentries and FF in my opinon because they get up in the Hydras face and zone them out from your voids. So you make them have to kite  you backwards, and if they don't zealot voidray in a straight up un microed fight will tear threw their hydras.

But yeah if you don't scout their fast 10min~ or so mutas your going to be hurting unless they have bad micro and then you will still be fine. Like if you don't scout it you only hope is to turtle make stalkers and defend until you have blink and enough stalkers. Its to late to make pheonixes you just have to hope that  you get lucky and they don't micro their mutas well and you can defend with photon overcharge and blink stalkers, until you get high templar out. Which like i said above archons and storm should allow you to take a late third with some cannons in you main and natural.