Bip39 Pub Dev. From this place ahead the seed may be created on paper or spoken more than phone and this opened up new, Actual physical ways of backing up the seed (multiple paper copies in different locations, long lasting copies on steel plates with excess security from fire/flood etcetera.). https://sites2000.com/story8646070/bitcoin-seed-phrase-generator-with-balance-the-definitive-guide-to-seed-phrase-generator-for-trust-wallet