You private key is stored locally, in your mobile device, and secured by secure enclave.
If you change to a new mobile, you will need to import your wallet into your new mobile. Process, remove the read only wallet from your new mobile, import your wallet through seed phrase or JSON.
If you delete your wallet from an old mobile device, without backing up the seed phrase, you will lose everything in that wallet, and there is no way to recover. This is a fundamental feature of decentralised blockchain wallets and its not in AlphaWallet's control.