Complex sentence: Phrynichus'main argument was that Alcibiades could not be trusted, for he didn't care about any form of government he only wanted a change in the Athenian constitution so he could then get his partisans in Athens to demand he be allowed to return.
Split into simpler sentences: Phrynichus'main argument was that Alcibiades could not be trusted, for he didn't care about any form of government. He only wanted a change in the Athenian constitution so he could then get his partisans in Athens to demand he be allowed to return.