I'll sound like a broken record regards to Kemp, but I really don't think Kemp offers immense upside.
For one, the ankle and hamstring problems - particularly the ankle - will inhibit Kemp's base stealing attempts. Second, Kemp's shoulder could be a problem. It was fully healed when he returned late last year, but he also had to have an offseason "cleanup" procedure. Third, Kemp could be seeing more frequent off days. He won't be rushed back to start the season and with Dee Gordon also figuring to get some time in OF, Kemp will probably play in 125-130 games tops. His plate discipline really wasn't all too impressive the last couple of seasons either, by combination of playing hurt and pressing.
I love Kemp as much as the next fantasy owner and Dodger fan. However, realistically, you're paying for a guy whose upside at this point is more of a 20-25/15 guy but could miss some games in the process.
In terms of this trade, Phillips has been declining the last several years, but he's still hitting almost 20 HR a year and for a solid average. He's also played 150 or so odd games a season and could hit second this year, which will decrease his RBI total and increase his runs scored. Phillips is boring, but you know what you get whereas Kemp's best-case scenario isn't all too different from Phillips' production IMO.