How do you sync a new iPad with an iPhone if you don’t have a computer?

Sync how ? If you mean contacts, Safari bookmarks, calendars you can use Settings > iCloud (or the email account settings, depending upon where the info is stored) to keep them in-line. If you mean syncing content (e.g. music, films etc.) from one device to the other you can't, you can't sync content from one iOS device to another, that requires a computer.