The Phase Tower, is the only tower in the game that can move. This aspect can make it extremely deadly in large numbers. They can be built at a safe range and moved forward into combat range as they are finished. The key to killing them lies in the fact that they are vulnerable for a short period of time after teleporting during which they take double damage. The simplest counter is the Mortar Tower, but be careful that the Phase Towers cannot teleport inside the Mortar's deadzone.
The highlight of this tower is the ability to move it after it's been placed. This is certainly useful for players who like to tower creep or if a defensive position requires dynamic changes. The other alternative is to simply use a more powerful tower and destroy-and-rebuild. Also be aware that moving the tower has the consequence of becoming more susceptible to damage. It is wise to move nearly-destroyed towers out of harm's way behind fresh towers rather than to move fresh towers forward, offensively (retreat over advance).