MMS is supported on Phoner app, and can be more effective than SMS in getting the point to your contacts more effectively. Follow the steps on How to send a text? to access your Message screen.
Note: Ensure that you have given permission for Phoner to access your Photos, so you can choose to send pictures from your photo library.
To send MMS text:
Tap on the camera icon on the left of the ‘Text message’ text field.