When I begin a text the addressees email comes up and not their cell phone number why?

sbm901 wrote:

Text messaging. Addressees email address comes up in selection list but not iPhone phone number!

The key word in your sentence above is "iPhone".

Since you said "iPhone", we know the recipient has an Apple product. That means the recipient can receive iMessages. And, in fact, the way you exchange messages with this person is iMessage, and not SMS text message through your cellular carrier.

Therefore, the person has chosen to use their Apple ID (which looks like an email address) to send/receive iMessages. Or perhaps you had some old thread you used to send or receive messages from this person previously that used their Apple ID.

You may regulate how your iMessages are sent and received at Settings > Messages > Send & Receive