Top is a 5-stroke contraction of standalone
尚 (8 strokes), the lower
口 dropped — the same shortcut as in
党.
尚 supplies the sound (shàng → cháng, regular zh-/ch- alternation). The three short top strokes form the ⺌ silhouette, which is why
尝 indexes under Kangxi #42
小 (xiǎo) by tradition.