If you have an iPhone and another iOS device, like an iPad, your iMessage settings might be set to receive and start messages from your Apple ID instead of your phone number. To check if your phone number is set to send and receive messages, go to Settings > Messages, and tap Send & Receive.
If you don’t see your phone number, you can link your iPhone number to your Apple ID so you can send and receive iMessages from your phone number. You can also set up Text Message Forwarding so you can send and receive MMS and SMS messages on all of your Apple devices.
If you still can’t send or receive messages, contact Apple Support.