How to sync numbers app with iPhone?

I just made a spreadsheet using the Apple's Numbers app and now I downloaded numbers for my iPhone but I want the spreadsheet from the iPad to be synced onto my phone. How though?

Make sure that the app is synced with iCloud on both devices
You can do that by going to settings -> (scroll all the way down) numbers -> use icloud

Along with Eduardo's answer, make sure both devices are using the same iCloud account.