I changed my apple id password and now my imessage says it comes from my email, not my phone number. My phone number is greyed out.

I changed my apple id password and now my imessage only comes from my icloud email address. It no longer comes from my phone number and sometimes will only be sent via text message. When I look at my profile for my icloud id on my phone the phone number is greyed out, it won't let me choose it. How do I fix this?