John Tyler, 10th President of the United States, was born in 1790 and died in 1862. His oldest surviving grandchild is still alive today at the time of writing, in 2024, at the age of 95. Tyler fathered children in his 60s, and one of his sons fathered children in his 70s. So there are regular humans around today whose grandparents were alive over 200 years ago.
'Kay. However, Phlox wasn't a senior citizen, nor even elderly by Denobulan standards (or human) to to have a grandparent who was alive two hundred years prior is something noteworthy.
Phlox was dead by the time the time displaced Enterprise in E2 caught up with present day, which was a 117 years later. Though they don't say how he died. Entirely possible it was not from old age.