Texts come thru from email instea of phone #

i have an iPhone 5 8.3 my texts come thru on the other end from my email address. some texts go thru from email & some from phone no. Not all textx show up as if they are being sent from an iPhone (color).

i Went to settings/messages/ send & receive & my email is checked. My phone no is grayed out & I cannot select it. I do not have the option to "start a new conversation" on that screen. How can I correct this?