I only use the BW to receive payments and view the balance, but you can easily sign with a dedicated phone. You leave one phone with the app and the PK (Payment Key), send a transaction from your WO phone, and then scan the QR code and sign the transaction from your other phone with the PK. Finally, scan the generated QR code again from the WO phone and the transaction is transmitted.
I only use the BW to receive payments and view the balance, but you can easily sign with a dedicated phone. You leave one phone with the app and the PK (Payment Key), send a transaction from your WO phone, and then scan the QR code and sign the transaction from your other phone with the PK. Finally, scan the generated QR code again from the WO phone and the transaction is transmitted.