Is it safe to delete my bitcoin wallet (coinomi) and restore it from 24 words phrase when ever i need it (once a year)
Yes. It is safe if you don't forget the seed.
You could also create a new wallet and send 1$ for example to one of its adresses, delete that wallet but keep the seed in mind and try to restore it. If you make a mistake, it's only 1$. If it works, you have the experience and don't need to worry.
By delete your wallet do you mean delete your account and .dat file? Thanks to BIP32 the seed/recovery phrase allows a user to back up and restore a wallet without needing any other information and can in some cases allow the creation of public addresses without the knowledge of the private key.
In other words your recovery phrase is equivalent to the private key so if you had a lost/deleted/stolen wallet then you would be able to recover it with the recovery phrase/seed.