not really if they are 1 base collosus all in, it's basically like a 4 gate that isn't countered by forcefields and with phix you rely heavily on the forcefields. I admit though it is really easy to kill most people's collosus before it stomps on your forcefields since they control it poorly. but if you miss their army moving across the map and see the collosus 4 gate at your natural then it's going to be tough if you do like a star robo 2 gate. you gotta make sure you know where his army is and kill the collosus even if it means sacrificing all your phix's (since you would have like double his probe count from all your phix kills it won't even matter)
and as to how many phix's i probably tend to get a lot more than 5, i guess it depends on each game; the map, how much dmg you do, what tech path etc. I don't stop making phix's until they go blink stalker archon or heavy stalker from lots of gates
there's no reason to expand vs 1base collosus if you open phoenix.
You can just wait for them to move out, pick up like half their damn mineral line, they are completely all in at this point and you're at 1 base. The have to engage up a choke (the ramp) with a stalker heavy army (since you went phoenix and forced them) and at that point you can snipe the collosus off and forcefield the ramp.
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