If you rely on your backup phrase what will happen if coinomi stop working?since you have no private key you won't be able to import backup phrase in all available wallets,only few like enjin supports coinomi backup phrases
Every wallet out there support the recovery phrase. if it doesn't, it is a shitty wallet, stay away (the only exception is bitcoin core)
The recovery phrase is a mathematical function that contains all the privatekeys of all possible generated addresses in your wallet, of all possible coins it supports now and will ever support in the future.
If coinomi supports a new coin tomorrow, the privatekey for that new coin will be contained in the recovery phrase.
Technology and math are like magic.