Confession Under Iconoclasm
The synaxarion entry for Saint Gregory states only that he was flogged and thrown into prison during the reign of Leo the iconoclast, and that he was left there without food until he died. No further biographical detail accompanies this notice.
His title of Confessor — paired with his rank as Hierarch — reflects this manner of suffering. In Orthodox usage a confessor is one who has suffered for the faith but was not martyred outright, distinguished from a martyr by having endured persecution and torture without being killed directly. Gregory's death from deprivation in prison, rather than by execution, is consistent with this designation.