Outer shelter radical - the indexing radical, picturing a sloping roof anchored to a wall. Anchors 庞 in the building/structure family with 店 shop, 库 storehouse, 庭 hall, 庙 temple. Frames the entry as something housed under a great roof.
Inside 龙 (simplified from 龍) supplies the sound lóng → páng via historical drift. The dragon image also reinforces 'huge, imposing' - a dragon-sized creature under a great roof gives a strong mnemonic for 'enormous.' Same simplified phonetic family: 笼 cage, 拢 gather, 聋 deaf.
