08-29-2016 10:02 AM
I recommend the section "Introduction to Survival Analysis Procedures" in the SAS/STAT documentation. It describes both procedures and compares them.
Briefly, LIFETEST provides a nonparametric estimate of the survival times. PHREG fits a (semi)parametric Cox model. In the Cox model you get parameter estimates that you can use to interpret the strength and significane of effects.