Interesting question. I'm not a judge and I'm not sure, so I should have not bothered answering probably.
That said, this is an opinion for the sake of speculation:
First off, other than the "I'm not a judge" bit, everything else there should be saying "don't post." If you're not sure, don't post, someone else who is sure will just need to follow up anyways. If you're already telling yourself "I shouldn't be posting this," then yes, you shouldn't be posting it. Just makes it look worse when you tell everyone you shouldn't be doing it while you are, in fact, doing it. People answering rules questions here is always welcome, when they know and are confident of their answer. Yes, sometimes people are confident but get it wrong anyways, I know I've done this myself. But when you're telling everyone you're not sure about it, it just creates extra posts since a definitive answer will be needed anyways, and the more the definitive answer gets buried among guesses and speculations and "I'm not sure"s the more likely it is to be missed.
As for the question at hand. The short answer is that in this case you'll have to pay 3 mana and 4 life.
It works the same as hybrid mana symbols. You don't pay "phyrexian mana." You pay either mana of the appropriate color, or 2 life.
At the time you determine alternate/additional costs, you also choose which half for each hybrid mana symbol, so for phyrexian symbols you choose either mana or life. So later when you are determining the total cost, you have "1 mana and 4 life." Trinisphere sees that the mana portion is less than 3 so raises that to 3.
My opponent has Trinisphere in play. I pay 1 mana and use 4 life to satisfy the Phyrexian portion of the casting cost. It seems to me like Trinisphere sees that I paid Phyrexian mana for the card and should be ok, but I talked to judge Abe Corson about it and he thinks that paying life for the Phyrexian mana is more like a cost reduction, so Trinisphere is not satisfied.
