My second option would be an airgapped pc but I also heard there are ways to extract private key from that airgapped pc. Assuming that your airgapped pc was infected already with a malware it can send electromagnectic signals to an infected phone and steal that key. And I heard there are other ways too.
4.My last question is , if I use the phone as an Airgapped device should I try to destroy bluetooth/wifi/antennas hardware (if there is any way) or is it safe to leave it as it is? I don't know if there is a way for the hacker to disable my airplane mode and making my phone go online to steal my private key.
It's much more likely to have a malware that just turns on the turned off network connection, rather than executing some sophisticated side-channel attacks. Also, stealing private keys and sending them to a remote server is just one way a malware can steal your coins - it could also try to inject its own addresses to your wallet, tamper with your RNG, try to replace the recipients address in transactions that you send. The point of airgap is not to just prevent malware from sending your private keys, the point is to prevent any malware from reaching such system.