A molecular phase inverter was a device that was capable of shifting the phase of matter.
Such a device was equipped on the USS Ranger, but had seen little use prior to 2381. The few occasions it was used, it restored phase-shifted objects displaced by transporter accidents or misconfigured warp fields by a few millicochranes. The Ranger commanding officer, Captain Peter Pachal, conceived of using the inverter to shift the vessel out of phase to pass through the adaptive shielding of a Borg cube, allowing the ship to detonate its stock of quantum torpedoes to defeat the enemy. Pachal was killed before the Ranger was ready, but first officer Jennifer Nero organized and successfully executed its use. (ST - Destiny novel: Gods of Night)
By 2409 the Romulan Republic had equipped its D'ridthau-class warbirds with these devices. (ST video game: Star Trek Online)