Your seed phrase is what that you can use to access your bitcoin on your wallet and to spend the coin. Many people are sending email that they should enter their seed phrase on a site. If they enter the seed phrase their, the bitcoin will be sent to another bitcoin address by the scammer.
Do not backup your seed phrase online because scammers can get to it online.
I have written down the seed phrase in multiple places because if one is lost or damaged, I will keep a backup through an alternative source. We have seen many incidents recently where some users have lost their phones or their phones have been damaged. Due to carelessness they have not taken care of their seed phrase and therefore they cannot recover the wallet. Saving it online or sending it to your email is a dangerous process because scammers are spreading their net and waiting for you to make a mistake.