Phayllus, a Phocian, brother of Onomarchus, whom he sicceeded as general of the Phocians in the Sacred War. He had already held important commands und r his brother, by whom he had been sent with an army of 7000 men to support Lycophron of Pherae against Philip of Macedon. (On that occasion he was unsuccessful, being defeated by Philip and driven out of Thessaly; but on the death of Onomarchus, in 352 BC, he appears to have succeeded without opposition to the chief command. He immediately set to work to restore the affairs of the Phocians. By an unsparing use of the vast treasures at his disposal, and by doubling the pay of his mercenaries, he quickly re-assembled a numerous army, in addition to which auxiliaries were furnished him by the Achaeans, Lacedaemonians, and Athenians, and the fugitive tyrants of Pherae, Lycophron and Peitholaus, also joined him with a body of mercenaries. The success of his military operations was, however, far from corresponding to these great preparations. He invaded Boeotia ; but was defeated in three successive actions, apparently none of them very decisive, as we next find him turning his arms against the Epicnemidian Locrians, and hostilities were carried on with alternations of success but no striking result. Meanwhile Phayllus himself was attacked with a lingering disorder of a consumptive kind, to which he fell a victim after a long and painful illness, A. c. 351. (Diod. xvi. 35-38, 61; Paus. x. 2. § 6 ; Harpocr. v. Φάϋλλος.) In this natural disease his enemies saw as plainly as in the violent deaths of his predecessors the retributive justice of the offended deities.

It appears certain that Phayllus had made use of the sacred treasures with a far more lavish hand than either of his brothers, and he is accused of bestowing the consecrated ornaments upon his wife and mistresses. (Diod. xvi. 61 ; Theopomp. ap. A then. xiii. p. 605; Ephor. ibid. vi. p. 232.) The chief command in his hands appears to have already assumed the character of a monarchy (Dem. c. Aristocr. p. 661), and began even to be regarded as hereditary, so that he left it at his death to his nephew Phalaecus, though yet a minor.