Victory lifted the home side to second in the table behind Ulster with 17 points from the boot of the unerring Aled Thomas also playing a huge hand in the win.
The Italian outfit's points came from a second-half try from Matteo Pratichetti - who also kicked a penalty - and eight points from Daniel Halangahu but Thomas' late penalty denied them what would have been just their second point of the season.
Scarlets have been among the early-season pace-setters in the RaboDirect PRO12 this season however they struggled to find their feet against Zebre in the first half.
Indeed but for some wayward kicking from the Italian's kicker Halangahu they could have found themselves more than 6-3 down at half-time.
It all started well for the centre with a 13th-minute penalty to make it 3-0 however he followed that up with back-to-back unsuccessful three-point attempts from the tee.
The half looked to be petering out until Scarlets centre Gareth Owen and Zebre back row Filippo Ferrarini received yellow cards for fighting in the 33rd minute.
Three minutes later the home side were level when Thomas kicked the first of five penalties but then Halangahu promptly landed a three-pointer of his own to send the teams in at half-time 6-3.
The second half was only four minutes old when Tito Tebaldi was send to the sin-bin for an off-the-ball push.
Led by scrum-half Gareth Davies the Scarlets started to spring into life and drew level with a Thomas penalty after 48 minutes.
Six minutes later the home side had the lead for the first time with another three-pointer and the momentum appeared to be with the Scarlets.
However on the hour mark the Italian outfit profited from some suspect defence from the home side - twice wasting opportunities to get hold of a loose ball - to cross for a try through Pratichetti.
Halangahu gleefully added the conversion and the Italian strugglers had the lead, 13-9.
Thomas hit back with another penalty to set up a grandstand finish with the clash poised to go either way.
It was an equally scrappy try that won it, again the defending side unable to deal with a rogue ball and once Phillips got his hands on it he was never going to caught.
The former Ospreys winger touched down in the corner with Thomas dead-eyed again to convert from out wide.
In what was a theme for the second-half a dominant Scarlets scrum earned them another penalty in the late stages which the fly-half promptly slotted.
It was a cruel blow for Zebre to deny them a bonus point and leave Scarlets to toast their sixth win from eight RaboDirect PRO12 games this term.
|Scarlets Score Card|
|Zebre Score Card|