to open, to spread out
捭 centers on the action of opening or spreading something out, often by hand. The two given meanings are closely related: to open something is to spread it apart.
捭 combines 扌 (hand) with 卑, which likely contributes the sound. The exact historical development of the compound is uncertain, but the hand radical suggests an action performed by hand.
The hand radical 扌 beside 卑 suggests a hand opening or spreading something. Imagine a hand pushing apart two halves of a folding screen to reveal what is behind.
For ハイ, picture a hand spreading open a high curtain: high -> ハイ, and the hand opens the way.
—