GoKawiilFirst, you'll need to secure your Android phone by marking it as lost. The best way to do this is to visit Find Hub on any device. Sign into your Google account, select the device in question, and choose Mark as lost. You will need to enter your device's PIN, pattern, or password.
Once you do this, your phone will log out of your Google account and remove all cards from your Google Wallet. You can also choose to display a message on your phone's lock screen with a contact number, so a good Samaritan can arrange for a safe return if they find the device. Once your phone is back in your hands, you can add your cards back to Google Wallet.
If you can't access your Google account for whatever reason, there's another way to protect your phone: Remote Lock. Go to android.com/lock from a browser on any device. There, enter your phone number, along with the security information required to identify yourself, to lock your Android phone. As long as the device is online (or once it connects to the internet), it will lock down so nobody can use it.
It's worth noting that Samsung Galaxy phones have their own layer of security if you have set up SmartThings Find. By default, it locks Samsung Wallet and suspends transactions until you can verify your identity. Go to the SmartThings Find website from any device, sign in to your Samsung account, select your phone, and select Lock. By default, this will lock access to Samsung Wallet and all your digital cards.