First and foremost, I won't be suggesting places to hide your seed phrase. Why? Because that defeats the purpose of a hiding place. If a hiding place becomes well known and popular, it's no longer hidden. It becomes a standard place a burglar or home invader would look every single time (like under a mattress). So we'll go over characteristics a hiding place should have to help you evaluate your current location or decide on one.
I'll make it clear right now. There is no best way to store your seed phrase. (I know, how dare you) Why? Because storing your seed phrase is unique to you. Like many things in life: something that works for you, might not work for someone else. Everyone is different. Storing your seed phrase is specific to what works for you and your situation.
A passphrase is different from your 12-24 word seed phrase. It is an optional, advanced security feature that allows you to create a new wallet by adding an additional word to a 12-24 seed phrase. It is supported by many wallets utilizing the BIP39 standard.