Your card numbers are not stored on the phone. The wallet app assigns each credit and debit card a virtual card number, sometimes referred to as a token, that is only associated with the digital wallet and mobile device you use.
When you use your device to pay, the wallet doesn’t send your actual credit or debit card number with your payment. Instead, it uses the virtual card number to represent your account info. Your card then is never exposed and neither is your checking account.
The apps require authorization via your fingerprint, passcode, or another security measure before completing the transaction. Additionally, to just have a card loaded the app will require the user to have their device security setup. Therefore if someone found your phone they couldn’t access your wallet without unlocking your phone.