We don't know anything more about him beyond what Herodotos tells us. The story of the anchor occurs in his description of the battle of Plataia, the decisive battle against the Persian invasion force in 479 BC. Since Herodotos wrote much of his work at Athens, he may well have heard the tale from someone who was there at Plataia. On the other hand, even Herodotos is unsure about the story, and offers an alternative version where Sophanes merely carried a shield with an anchor painted on it.

From that town [Dekeleia in Attika] was Sophanes, who now was the best Athenian fighter in the battle, and about him two tales are told. According to the first, he bore an iron anchor attached to the belt of his cuirass with a chain of bronze. He would cast this anchor whenever he approached his enemies in an attack so that the enemy, as they left their ranks, might not be able to move him from his place. When they were put to flight, it was his plan that he would pull up his anchor and so pursue them. So runs this tale. The second contradicts with the first and relates that he wore no iron anchor attached to his cuirass, but that his shield, which he constantly whirled round and never held still, had on it an anchor as a device.

-- Hdt. 9.74

As for Sophanes himself, he is very likely to be a real person. Herodotos mentions him elsewhere too (at 6.92.3). When the Athenians were besieging Aigina in the late 490s BC, the Argive commander Eurybates, who came to the aid of the Aiginetans, supposedly defeated 3 Athenians in single combat before Sophanes stepped up as the fourth challenger and killed him. Herodotos brings up this story again at Plataia after describing the business with the anchor (9.75). Interestingly, he did mess up Sophanes' patronym; he is initially called the son of Dekeles, but at Plataia he is suddenly the son of Eutychides.

Herodotos also notes that he was one of the generals in charge of the failed Athenian attempt to settle a colony in Thrace in 465 BC. He was killed by the men of a local tribe. It would be very strange indeed if Herodotos simply invented the name of one of Athens' ten generals for 465 BC, especially when there were records he could check, Athenians he could talk to, and presumably stories going around about the disastrous expedition.