The Phased Waterproof Pipe is a pipe designed to interface with Buildcraft to remotely transport liquids such as Water, Lava, Oil, and Fuel generated by Buildcraft machines and collected from the environment through the use of a Pump.
It is essentially a remote liquid transport pipe and can be configured to broadcast or send/receive liquid to a specific channel/wavelength anywhere in the world (as long as the chunk is loaded). New in Tekkit Lite it will also transport fluids from the nether into the overworld making it useful to teleport lava back to your base.
Pumping from the Nether
Phased waterproof pipes can be used to pump lava from the Nether. Dimensional Anchors are neccessary to keep the chunks loaded, though. Here is an example of a pumping station located in the Nether:
Note how the machines and pipes are enclosed in glass. That way, the player can see outside of the enclosure to check if any Ghasts are nearby when entering or exiting, so that the facility is not blown up by their fire balls (Ghasts cannot see through glass).
An example of the damage that pumps in the nether can cause:
An example of how to set up the power conversion facility on the other end of the phased pipes: