Both headword and gloss are problematic.
Other lexica (references at Photius pi857 Theodoridis) spell the headword ph/luc (with r(aga/s or r(wga/s as the gloss), but alphabetical order guarantees the alpha here. The Etymologicum Magnum cites ph/lac in the etymology of phlaki/zw (cf. pi 1505). But "neither ph/lac nor the simple phlaki/zw certainly existed" (LSJ s.v. prophlaki/zw).
The glossing term r(aga/s (oxytone, not paroxytone as here: cf. sigma 939) or r(wga/s (cf. rho 242) means a crack or fissure in the earth or elsewhere (related to the verb r(h/gnumi). According to Hesychius, it can also be equivalent to r(wga/s meaning a cluster of grapes.