Google gives every Android user 14GB of free Drive cloud storage, unless they changed that policy. It sounds like you have Backup To Drive enabled in your phone and are creating phone backups often to your Drive storage. If so, deleting backups from Drive won't affect your current phone. You'll just delete old backups. Would you restore from an old backup or a recent one? Probably a recent one. So deleting the old ones should be OK. Your phone will function fine independent of Google Drive, it doesn't "need" Drive to operate, those are probably just lots of old backups taking up space.
But that's also weird, my backups only take up minimal space. And that's years of backups. How often are you manually selecting the Backup Now option?