Can't Recieve messages on iPad unless I'm already in conversation, looked at my settings and noticed that the Send and Recieve is showing email and not my phone number. What do I tap on to change this ?

When receiving messages I am only able to get them on my iPhone 6+ but not my iPad 3 unless I am already in conversation on my iPad. Went to my settings and checked my Send and Recieve and it's showing my email address instead of phone number. How do I make the switch from email to phone number? There is nothing thats letting me make the switch. Don't know if that is the problem