How safe is it to only back up on iCloud Want to know if iCloud backup you can do on your phone will keep stuff safe. Would do on iTunes but laptop unfortunately broke down. Is it safe to backup your stuff onto iCloud and can you successfully get it back after phone is reset?
iCloud is pretty safe (and designed to set-and-forget), but cases of corrupt or unusable backups have been seen on both iCloud (1), (2) and iTunes.
It is a good idea to have both local and remote backups, and backup often, so in case of a corrupt backup you have a recent older copy.  

Also, local copies are much faster to restore, so ideally do one before upgrading or restoring your phone.