With Electrum wallet, in its newest versions, the wallet software by default settings will give users Segwit addresses.
If you have a legacy seed phrase and you import it, electrum will give you legacy addresses.
You can't generate segwit addresses from a legacy seed phrase at all.
If you want to have Legacy addresses, you can import your wallet seed, and choose BIP39. You can type the mnemonic seed, choose BIP39 to try. If it accepts, you will have three options to import, as written in this guide,
Restoring your standard wallet from seed.You can't specify the addresses type, if the seed phrase has been generated by electrum. As already said by Charles-Tim, electrum seeds contain a version number which determines the seed type.
If you enter your electrum's seed as a BIP39 seed, you can specify the address type, but that will lead to a different wallet.