How to transfer ringtones downloaded from Cydia from my iPad to my iPhone?

With out a computer.

Download Wireless Transfer App from App Store. It is free for a limited time.

In my opinion, you can use the iCloud to transfer ringtones from iPad to iPhone. There's also another way that you could use the bluetooth to transfer, too.

Try Tipard iPhone Transfer which allows you transfer music/movie/Pictures/TV Shows/Podcast/iTunes U/eBooks/Camera Roll/Ringtone/SMS/Contacts/Voice memos/Camera shot files between any two Apple devices.