Consider Phlebas isn't really representative of his other Culture work. It's him trying to present an objective counterviewpoint about his personal dream space communist utopia, which he explores in detail in every other Culture book, but it ends up being a story about unlikable assholes blasting their way through a series of impressive set-pieces. It's hard to love it.

I would recommend that you try either Player of Games and/or Use of Weapons. PoG is his most conventional narrative and it's just fun. UoW is non-linear and mindfucky in the Banks tradition. Most people consider these two books his best SF.