You can only delete your account if you registered it manually or linked it to a social network profile. You can't delete an account that was registered to a phone number.
If you have a Yandex account that you use to log into other services, then you will lose data saved on all the personal services connected to that account (Mail, Disk, etc.) if you delete it. Additionally, you will permanently lose your music library if you delete your account.
To learn more about how to delete your Yandex account, go to the Delete account section of Help for Yandex.Passport.
Deleting your account does not cancel your subscription automatically. If you have a current subscription, you should cancel it manually first.
If you purchased your subscription through the App Store or on Google Play, you can cancel it there even after you delete your account. If you deleted your account and forgot to cancel a subscription that you placed using the web version of the service, contact customer support.