The headword, dative plural of the adjective in question, is not otherwise attested in this *Kubeli/ois form, but, as Adler notes, Toup drew attention to the (unique) instance of *Kubelei/ois in Synesius, In Praise of Baldness PG 66.1204d.
The words for Cybele, the Phrygian and Roman Great Mother (see kappa 2586), here have a short epsilon in the second syllable. The Galli were her priests who had castrated themselves to bring themselves closer to their goddess and to the presexual nature of the origin of life, as described by St. Hippolytus in his account of the Naassene heresy.
[1] From an epigram of Rhianus (fr.67 = Greek Anthology 6.173.3). The adjective should be spelled with two lambdas: see gamma 23. On this epigram, wherein an attendant of Kybele dedicates her hair upon retiring from the cult, see Gow and Page (vol. I, 176), (vol. II, 506-507), and further excerpts at omicron 540 and theta 7.