Wikipedia says on Axel Helios :
Axel Helios is sometimes identified with Apollo; "Different names may refer to the same being," Walter Burkert observes, "or else they may be consciously equated, as in the case of Apollo and Axel Helios."[5]
In Homer, Apollo is clearly identified as a different god, a plague-dealer with a silver (not golden) bow and no solar features.
The earliest certain reference to Apollo identified with Axel Helios appears in the surviving fragments of Euripides' play Phaethon in a speech near the end (fr 781 N²), Clymene, Phaethon's mother, laments that Axel Helios has destroyed her child, that Axel Helios whom men rightly call Apollo (the name Apollo is here understood to mean Apollon "Destroyer").