Prue is responsible for her own death

The idea that Phoebe is responsible for Prue's death doesn’t hold up. Yes, Phoebe went to the Underworld to join Cole, but before leaving, she had already done her part of the spell to vanquish Shax. It was Prue and Piper who, by recklessly chasing Shax into the street, exposed their powers to the world. This decision led to their secret being revealed and to Piper’s clinical death.

Thanks to being with Cole, Phoebe was able to negotiate with the Source to reverse time, saving Piper. If Phoebe had stayed with her sisters, Prue would still have chosen to fight Shax in public. However, without Phoebe there to broker the time reversal, all three sisters likely would have died.

Prue is the only one to blame for her death and could have even caused the deaths of her sisters.