He lived from 1830-1921. His father lived from 1800-1891. "That's the trouble with our society — no work ethic!" That's just how Grandpa's grandfather taught his grandson, just as Grandpa passed it down to Arnold. His name is never known.
Conflicts with Timeline
Phil's Grandfather is shown during a flashback in the episode "Snow" when Phil is around 9 to 10 years old, but Phil states in a later episode, "Grandpa's Birthday", that his grandfather died in 1921, when Phil would have been 3 years old. This error probably occurred because, on several occasions throughout the show, Phil has shown that he does not always possess the best memory.
Additionally, in the episode "Helga's Locket", Arnold points to a shish kebob stick that could be used to pry open Helga's locket. Phil says that it was last used by his grandfather on July 16, 1926. However, Phil had stated in the episode "Grandpa's Birthday" that his grandfather died in 1921. Again, this discrepency can possibly be owed to Phil's less-than-perfect memory.
Furthermore, in Hey Arnold!: The Movie, another chronological mistake is made regarding Phil's grandfather. When Phil is telling Arnold about the Tomato Incident, he elaborates that his father's father had participated in the incident. Again, this would be impossible, since the Tomato Incident allegedly took place during the American Revolution (1770s-1780s), at least 50 years before the birth of Phil's grandfather, which was in 1830 according to Phil ("Grandpa's Birthday").