Can you plug your iphone into ipad and use internet through phone

If your phone's carrier supports the personal hotspot function : http://support.apple.com/kb/HT4517 - the iPad should see the phone as a wifi network

If you don't get the Settings > General > Cellular > Personal > Hotspot option on your phone then you may need to check with your carrier to see if they support it, and if they do whether you are on the correct tariff with them.