I don't think reviewers were listening to the dialogue in this movie well enough, or perhaps they didn't understand the references.

Two of the male spartans were flirting with each other. In one scene, the youngest son of the general who has come to fight alongside his father in battle flirts with another warrior. They flirtingly joke about selling the other's "backside to a Thebian" - the Thebians lived in Thebes - the place that spawned the renown Sacred Band of Thebes, the homosexual fighting force - 6,000 Thebians crushed the military prestige of the Spartans (11,000 of them) at the Battle of Leuctra.

In a later scene, just before the younger man is killed, the other warrior comes to his rescue saying "I've come to watch your backside." to which the younger man lovingly replies "Not now, I'm fighting." The only way you could consider 300 phobic is if you perceived 7 foot tall Xerxes, who had a boomingly low voice, to be feminine which if you are effete and you wear make-up you probably related to him, but for masculine gay guys, the two flirting Spartans are the ones you related to - so the movie is fey-ophobic rather than homophobic.