Do you use the standard "Message" app? In addition to the message service (SMS / MMS) using the address of the communication carrier, Apple's own "iMessage" is supported. I can communicate. Other features such as "animoji" that move according to facial expressions are also available, and it can be said to be one of the apps that represent the iPhone.
It is the message application, but multiple e-mail addresses may be displayed on the screen that appears when you tap "Settings"-> "Message"-> "Send / Receive". In this screen, in addition to the Apple ID currently in use, in the top "Contacts and …" field above, the phone number / email address that is allowed to use iMessage, and the "New Chat Originator" at the bottom In the field, select the phone number / e-mail address displayed on the other party's screen when starting a new communication.
In the "Contacts and …" field, select the messages that are sent to you and that you want to receive on your current iPhone. If you uncheck the email address, iMessages sent to that email address will not be received by the iPhone.
By applying this mechanism, iMessage can be used properly on multiple terminals. Since you cannot uncheck the phone number on the iPhone, you will always receive iMessages sent with the phone number as the destination, but you can uncheck all email addresses. IMessages for phone numbers can be used for iPhone, and iMessages for email addresses can be used for Mac / iPad.
Of course, you can check all items and receive all iMessages for your phone number / email address. Set it up so that you can use it easily.