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.
There's a reason why it's called a seed phrase in the first place, it means that it should stay hidden. A lot of people wonder why their assets gets stolen, this makes them start saying things like the wallet is a scam but whereas they are the ones that are just being careless. Backing up your seed phrase online can give others access to your wallet. There are several ways to maintain maximum security of your seed phrase and I don't suggest that it should be saved on your mobile device if you are the type of person that gives other people your phone. You can write it out and keep it in a place that you can always see and is not within people's reach