The phase where two new nuclear envelopes form is telophase, the final stage of mitosis.

Here's why:

* Mitosis: This is the process of cell division where a single parent cell divides into two identical daughter cells.

* Telophase: During telophase, the chromosomes have reached opposite poles of the cell, and the mitotic spindle disassembles.

* Nuclear Envelope Formation: The fragments of the original nuclear envelope that were broken down in prophase and prometaphase begin to reassemble around the chromosomes at each pole. This forms two new, distinct nuclear envelopes, one for each daughter cell.

So, the formation of two new nuclear envelopes marks a key step in the completion of cell division during telophase.