A further witness to the Borborians or Phibionites mentioned by Epiphanius is to be found in the catalogue of heresies by Filaster or Philaster in his Diversarum haereseon liber (PG12, col. 1186):
Alia est haeresis Borborianorum, qui vitiis implicati saeculi, et malis concupiscentiis servientes, non sperant judicium futurum, sed potius carnalem saeculi concupiscentiam laudant. Hi itaque in coenum euntes, et inde obliti de coeno facies et membra sua deformantes, eadem re cunctis velut culpandam Dei creaturam demonstrantes: cum illa vorago culparum, et vitiorum perniciosa damnatio ex hominum voluntate, non Legis divinae permissione descenderit.
73. The Borborians.
Otherwise is the heresy of the Borborians, who, entangled in the vices of the times, and enslaved to evil lusts, do not look forward to a future judgement, but rather approve the bodily lust of today. And so these, entering into filthiness, and so [their] appearance forgetful of filth and defiling their limbs, [do] everything in the same way, as if showing off a creature that must be condemned by God: since such an abyss of crimes against chastity, and the certain damnation of vices voluntarily carried out by humans, will not be lessened by the sanction of the divine law.
Filaster was bishop of Brescia in 381 AD. A google search suggests that his work is at least partially dependent on Epiphanius; indeed Augustine compared the two works in Ep.222, and didn’t think much of Philaster’s version
Even if we did not know this theory – I was unable to learn what data requires this conclusion -, I would tend to feel that this is not an independent witness. Nothing about this passage suggests personal knowledge of the cult, to my eyes, but rather the abbreviation of some other written source.