Believe it or not, Phillips is actually a significant offensive upgrade over last season's primary backup, Ken Huckaby. Phillips by no means had a good season (.238/.287/.363 while playing half his games in pitcher-friendly Dodger Stadium), but Huckaby's was historically awful. In fact, in 87 at-bats he posted a line of .207/.250/.253, good for an OPS+ of 34. Granted, that's a small sample size, but Huckaby's career line of .223/.256/.282 in 422 AB is much better.
One glaring red flag, however, is that Phillips only threw out 16% of would be base stealers (19 CS/97 SBA). Ken Huckaby, on the other hand, threw out 40% (10 CS/22 SBA). Since Gregg Zaun has trouble throwing out runners (19% last season), the backup should be able to adequately fill in for him defensively should the need arise. Based on his past performance, Phillips wouldn't fulfil that obligation.
In the end, I hope neither Phillips nor Huckaby is relied upon extensively next season. My hope is that Guillermo Quiroz finally lives up to his potential and supplants Zaun in the coming seasons. However, since Quiroz cannot be counted on at the moment, I have no problem with the Phillips signing. If he performs well in spring training and makes the team as a backup, then fine. If not, it won't hamper the team in any major way. It's a very low-risk signing.