Right phonetic
冒 supplies the full sound mào with no drift, and a strong layer of meaning:
冒 itself originally pictured a hat over an eye (
冃 +
目), the picture of headwear. So
帽 is essentially 'hat' written twice — first the cloth radical, then the older hat-graph
冒 — to disambiguate after
冒 took on extended senses (risk, brave).