Left phonetic
巠 supplies the sound (jīng drifted to jǐng, just a tone shift).
颈's left side is the contracted 5-stroke form; the standalone
巠 character keeps the fuller traditional 7-stroke shape with loom-threads above
工. The jīng family
经 (classic; manage),
径 (path),
茎 (stem) all use this same contracted left side, visually shorter than the traditional glyph but conceptually identical.