I am a Phd. student at Lovely Professional University.
These are the eligibility requirements for admission into LPU for a Phd-
The final selection for PhD admission is based on the performance of a candidate in the entrance test (70% weightage) and interview (30% weightage).
Thus, only PG degree holders are eligible for admission into the Phd. program at LPU. But I would suggest that you call the admissions office to enquire if in any case you can seek admission into Phd. at LPU as a PG diploma holder.