Assuming both devices are linked to the same Apple ID go to the iTunes store app on the iPhone, tap More, the Purchased, then Music, then "Not on this iPhone". Or connect the iPad to your computer, then choose "Transfer Purchases" from the iTunes File menu. Then connect the iPhone to the same computer and sync it.
There is another way...
plug your iPad into your computer and open up iTunes
Click on this iPad and then in the bottom right click sync
This should sync the music from your iPad to your laptop, computer
then plug your iphone 5 in and click iphone in top right corner
then click music and then sync
This will sync the music that you put from your ipad to your computer now to your iphone!
Hope This Helped!
<Edited by Host>