Meat-flesh radical on the left — looks like 月 moon but is the side-form of 肉. It files 脐 in the body-parts family with 胸 chest, 肚 belly, 腰 waist. A navel is a feature of the abdomen, and the radical pins the meaning to the body wall.
Right side 齐 supplies the qí sound exactly. The 'even; aligned' meaning has a faint echo — the navel sits dead-centre on the belly, the body's natural midpoint — but the dominant role is phonetic. Same series: 剂 dose, 济 cross-river.
