IGN has a nice article examining the History of Sega. It is a very long piece at 11 pages. Most of it deals with Sega's consoles and marketing strategy. There's also some interesting stuff about their early years. Did you know the company was founded by Americans?
There isn't much focus on Sega's games, though Sonic gets mentioned plenty. Phantasy Star 1 gets a briefly name drop on the third page, but I didn't see any other mention of the series in a quick skimming over.