Why the mobile phone in the bell jar needed to be sitting on a sponge when the air was removed?

The mobile phone in the bell jar needed to be sitting on a sponge to provide cushioning and support, preventing it from directly contacting the glass surface. This arrangement helps absorb any vibrations and reduces the risk of damage to the phone as the pressure inside the jar changes. Additionally, the sponge can help maintain stability, ensuring that the phone remains in place during the air removal process.