Theodosios 12 was bishop of Chonai, also called Kolossai and Psonous, in Phrygia Pacatiana; his name is also recorded as Dositheos; in 787 he attended the Second Council of Nikaia (the Seventh Ecumenical Council) and was probably present at all eight sessions, from 24 September to 23 November 787: Mansi XII 998-XIII 486. In the list of those present at the first session he is styled Θεοδοσίου ἐπισκόπου Χώνων: Mansi XII 998. In the list of those present at the seventh session he is styled Δοσιθέου ἐπισκόπου Ψόνων ἤτοι Κολασσῶν (sic): Mansi XIII 372 (the Latin version, at XIII 371 reads "Sositheo episcopo Psonuntensium, sive Colasson"). In the list of names from the second session he is styled Θεοδόσιος ὁ ὁσιώτατος ἐπίσκοπος Χώνων: Mansi XII 1106. In the list from the fourth session he is styled Δοσίθεος ἐπίσκοπος Ψονοῦντος ἤτοι Κολασσάεων: Mansi XIII 148. In the list from the seventh session he is styled Δοσίθεος ἀνάξιος ἐπίσκοπος Χώνων: Mansi XIII 393. For the identity of Chonai and Kolossai, see Ramsay, Historical Geography, pp. 135, 429. The name Psonous seems unrecorded elsewhere. It is uncertain if his real name was Theodosios or Dositheos. At the second session he supported the traditional veneration of icons as described in statements from pope Hadrian I (Hadrianos 1) and condemned iconoclasts: Mansi XII 1106. At the fourth session he subscribed the statements read out from the Fathers in support of the veneration of icons: Mansi XIII 148. At the seventh session he subscribed the statement of the faith adopted by the Council: Mansi XIII 393.

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