Hey there,
When you call one of your contacts, you don't need to choose which number to use every time. By default, your iPhone uses the same number that you used the last time you called that contact. If you haven't called that contact, your iPhone uses your default number. You can also specify which number to use for your calls with a contact. Follow these steps:
- Tap the contact.
- Tap Preferred Cellular Plan.
- Tap the number you want to use with that contact.
You can choose the number you want to call from either through the contact you want to call through the option you see in the picture:
Or when you type the number you want to call:
For more info see this article ☞ Using Dual SIM with an eSIM - Apple Support