The seed phrase is saved in the wallet file, only if it has been generated by electrum itself.
Sorry but I'm not sure about this! Because if that was true then how is Electrum going to generate the key pairs of the imported wallet (BIP39) every time it loads?
What I know is that Electrum does not save the private keys of individually imported
addresses in the current wallet files. For imported seeds, I believe (and correct me if am wrong) it creates a new wallet file in which it saves the bip39 seed.
It will not save the seed phrase but saves the master private key.
This first one is for Electrum:
You can see the seed phrase.
The second one is for BIP39
There is no seed phrase there but you can see the master private key.
I think it is well explained now.
Anyone that wants to steal my bitcoin can go and steal it now. Waste of time