What happens if I take damage with Worship out while at negative life?
You will get the 5 poison counters if you have Phyrexian Unlife, and lose 5 life if you have Platinum Angel.
The card Serra the Benevolent has an ultimate ability that creates an emblem with Worship's ability. It has a ruling that says this:

If you have less than 1 life and somehow haven’t lost the game, damage dealt to you reduces your life total further below 0 (as normal).

So, Worship has no effect if you have less than 1 life, so damage will be dealt to you as normal and Phyrexian Unlife will modify it as normal.