Looking for a way to transfer BTC/BCH with private key using mobile device (iOS or Android).

Hello cryptonians. As far as we know the most secured way for transferring and storing crypto is the “paper” random generated private key. Let’s say I have generated one using the Bitcoin core offline. The next step is to transfer BTC / BCH using my mobile device. In order this to happen I have to install the Bitcoin core on the device, sync with the blockchain and after that to create a payment transaction. As we know the chain is few hundred GB 200-300. So instead downloading the full chain as lack of storage and no need to have it my phone, am looking a safe and secure way to create a transaction. Any ideas?