It would be beneficial to omit the area code for countries that do not use it.
While it's not certain whether every country has an area code, even assuming that each technically does, its inclusion can be confusing for end-users. For example, an example of Swiss phone number could be +41 12 345 67 89, with no area code required.
Implementing a feature that allows you to decide when to include an area code would greatly simplify data entry and intuitivity for users
Summary
It would be beneficial to omit the area code for countries that do not use it. While it's not certain whether every country has an area code, even assuming that each technically does, its inclusion can be confusing for end-users. For example, an example of Swiss phone number could be +41 12 345 67 89, with no area code required. Implementing a feature that allows you to decide when to include an area code would greatly simplify data entry and intuitivity for users